Vertically-alligned (va) liquid crystal display device

ABSTRACT

A vertically alignment mode liquid crystal display device having an improved viewing angle characteristic is disclosed. The disclosed liquid crystal display device uses a liquid crystal having a negative anisotropic dielectric constant, and orientations of the liquid crystal are vertical to substrates when no voltage being applied, almost horizontal when a predetermined voltage is applied, and oblique when an intermediate voltage is applied. At least one of the substrates includes a structure as domain regulating means, and inclined surfaces of the structure operate as a trigger to regulate azimuths of the oblique orientations of the liquid crystal when the intermediate voltage is applied.

This is a Divisional of application Ser. No. 12/070,524, filed Feb. 19,2008, which is a Continuation of application Ser. No. 11/600,859, filedNov. 16, 2006, which is a Continuation of Ser. No. 09/689,928, filed onOct. 12, 2000, which is now U.S. Pat. No. 7,224,421, which was issued onMay 29, 2007, which is a Divisional of application Ser. No. 09/097,027,filed on Jun. 12, 1998, which is now U.S. Pat. No. 6,724,452, which wasissued on Apr. 20, 2004.

BACKGROUND OF THE INVENTION

The present invention relates to a liquid crystal display (LCD), or moreparticularly, to a technology for realizing orientation division for avertically-aligned (VA) LCD.

Among flat-panel displays enjoying image quality equivalent of the oneoffered by the CRT, it is a liquid crystal display (LCD) that has beenmost widely adopted nowadays. In particular, a thin-film transistor(TFT) type LCD (TFT LCD) has been adapted to public welfare-relatedequipment such as a personal computer, word processor, and OA equipment,and home electric appliances including a portable television set, andexpected to further expand its market. Accordingly, there is a demandfor further improvement of image quality. A description will be made bytaking the TFT LCD for instance. However, the present invention is notlimited to the TFT LCD but can apply to a simple matrix LCD, a plasmaaddressing type LCD and so forth. Generally, the present invention isapplicable to LCDs which include liquid crystal sandwiched between apair of substrates on which electrodes are respectively formed and carryout displays by applying voltage between the electrodes.

Currently, a mode most widely adopted for the TFT LCD is anormally-white mode that is implemented in a twisted nematic (TN) LCD.The technology of manufacturing the TN TFT LCD has outstandinglyadvanced in recent years. Contrast and color reproducibility provided bythe TN TFT LCD have surpassed those offered by the CRT. However, the TNLCD has a critical drawback of a narrow viewing angle range. This posesa problem that the application of the TN LCD is limited.

In an effort to solve these problems, Japanese Examined PatentPublication Nos. 53-48452 and 1-120528 have proposed an LCD adopting amode referred to as an IPS mode.

However, the IPS mode suffers from slow switching. At present, when amotion picture representing a fast motion is displayed, drawbacksincluding a drawback that an image streams take place. In an actualpanel, therefore, for improving the response speed, the alignment filmis not rubbed parallel to the electrodes but rubbed in a directionshifted by about 15°. However, even when the direction of rubbing isthus shifted, since the response time permitted by the IPS mode is twicelonger than the one permitted by the TN mode, the response speed is verylow. Moreover, when rubbing is carried out in the direction shifted byabout 15°, a viewing angle characteristic of a panel does not becomeuniform between the right and left sides of the panel. Gray-scalereversal occurs relative to a specified viewing angle.

As mentioned above, the IPS mode that has been proposed as analternative for solving the problem on the viewing angle characteristicof the TN mode has the problem that the characteristics offered by theIPS mode other than the viewing angle characteristic are insufficient. Avertically-aligned (VA) mode using a vertical alignment film has beenproposed. The VA mode does not use a rotary polarization effect which isused in the TN mode, but uses a birefringent (double refraction) effect.The VA mode is a mode using a negative liquid crystal material andvertical alignment film. When no voltage is applied, liquid crystallinemolecules are aligned in a vertical direction and black display appears.When a predetermined voltage is applied, the liquid crystallinemolecules are aligned in a horizontal direction and white displayappears. A contrast in display offered by the VA mode is higher thanthat offered by the TN mode. A response speed is also higher, and anexcellent viewing angle characteristic is provided for white display andblack display. The VA mode is therefore attracting attention as a novelmode for a liquid crystal display.

However, the VA mode has the same problem as the TN mode concerninghalftone display, that is, a problem that the light intensity of displayvaries depending on the viewing angle. The VA mode provides a muchhigher contrast than the TN mode and is superior to the TN mode in termsof a viewing angle characteristic concerning a viewing angle or aviewing angle characteristic, because even when no voltage is applied,liquid crystalline molecules near an alignment film are aligned nearlyvertically. However, the VA mode is inferior to the IPS mode in terms ofthe viewing angle characteristic.

It is known that viewing angle performance of a liquid crystal displaydevice (LCD) in the TN mode can be improved by setting the orientationdirections of the liquid crystalline molecules inside pixels to aplurality of mutually different directions. Generally, the orientationdirection of the liquid crystalline-molecules (pre-tilt angles) whichkeep contact with a substrate surface in the TN mode are restricted bythe direction of a rubbing treatment applied to the alignment film. Therubbing treatment is a processing which rubs the surface of thealignment film in one direction by a cloth such as rayon, and the liquidcrystalline molecules are orientated in the rubbing direction.Therefore, viewing angle performance can be improved by making therubbing direction different inside the pixels.

Though the rubbing treatment has gained a wide application, it is thetreatment that rubbs and consequently, damages, the surface of thealignment film and involves the problem that dust is likely to occur.

A method which forms a concavo-convex pattern on an electrode is knownas another method of restricting the pre-tilt angle of the liquidcrystalline molecules in the TN mode. The liquid crystalline moleculesin the proximity of the electrodes are orientated along the surfacehaving the concavo-convex pattern.

It is known that viewing angle performance of a liquid crystal displaydevice in the VA mode can be improved by setting the orientationdirections of the liquid crystalline molecules inside pixels to aplurality of mutually different directions. Japanese Unexamined PatentPublication (Kokai) No. 6-301036 discloses a LCD in which apertures areprovided on a counter electrode. Each aperture faces a center of a pixelelectrode and oblique electric fields are generated at a center of eachpixel. The orientation directions of the liquid crystalline moleculesinside each pixel are divided into two or four directions due to theoblique electric fields. However, the LCD disclosed in JapaneseUnexamined Patent Publication (Kokai) No. 6-301036 has a problem thatits response (switching) speed is not enough, particularly, a responsespeed for transition from a state in which no voltage is applied to astate in which a voltage is applied is slow. A cause of this problem ispresumed that no oblique electric field exists when no voltage isapplied between the electrodes. Further, because a length of each areahaving continuously oriented liquid crystalline molecules in each pixelis a half of a pixel size, a time for all liquid crystalline moleculesin each area to be oriented in one direction becomes long.

Further, Japanese Unexamined Patent Publication (Kokai) No. 7-199193discloses a VA LCD in which slopes having different directions areprovided on electrodes and the orientation directions of the liquidcrystalline molecules inside each pixel are divided. However, accordingto the disclosed constitutions, the vertical alignment film formed onthe slopes are rubbed, therefore, the VA LCD disclosed in JapaneseUnexamined Patent Publication (Kokai) No-7-199193 also has theabove-mentioned problem that dust is likely to occur. Further, accordingto the disclosed constitutions, the size of the slopes is a half of thepixel, therefore, all liquid crystalline molecules faces the slopes areinclined, a good black display cannot be obtained. This causes areduction of contrast. Further, inclination angles of the slopes aresmall because two or four slopes are provided across each pixel. It isfound that the gentle slopes cannot fully define the orientationdirections of the liquid crystalline molecules. In order to realizesteep slopes, it is necessary to increase a thickness of a structurehaving slopes. However, when the thickness of the structure becomeslarge, charges accumulated on the structure becomes large. This causes aphenomenon that the liquid crystalline molecules do not change theirorientations when a voltage is applied due to the accumulated charges.This phenomenon is so-called a burn.

SUMMARY OF THE INVENTION

As described above, there are some problems to realize a division oforientation directions of the liquid crystalline molecules for improvingthe viewing angle performance in the VA LCD.

An object of the present invention is to improve a viewing anglecharacteristic of a VA liquid crystal display, and to realize a VAliquid crystal display exhibiting a viewing angle characteristic that isas good as the one exhibited by the IPS mode or better than it whilepermitting the same contrast and operation speed as the conventionalliquid crystal displays.

According to the present invention, in the VA mode employing aconventional vertical alignment film and adopting a negative liquidcrystal as a liquid crystal material, a domain regulating means isincluded for regulating the orientation of a liquid crystal in whichliquid crystalline molecules are aligned obliquely when a voltage isapplied so that the orientation will include a plurality of directionswithin each pixel. The domain regulating means is provided on at leastone of the substrates. Further, at least one of domain regulating meanshas inclined surfaces (slopes). The inclined surfaces include surfaceswhich are almost vertical to the substrates. Rubbing need not beperformed on the vertical alignment film.

In the VA LCD device, when no voltage is applied, in almost all regionsof the liquid crystal other than the protrusions, liquid crystallinemolecules are aligned nearly vertically to the surfaces of thesubstrates. The liquid crystalline molecules near the inclined surfacesalso orientates vertically to the inclined surfaces, therefore, theliquid crystalline molecules are inclined. When a voltage is applied,the liquid crystalline molecules tilt according to an electric fieldstrength. Since the electric fields are vertical to the substrates, whena direction of tilt is not defined by carrying out rubbing, the azimuthin which the liquid crystalline molecules tilt due to the electricfields includes all directions of 360°. If there are pre-tilted liquidcrystalline molecules, surrounding liquid crystalline molecules aretilted in the directions of the pre-tilted liquid crystalline molecules.Even when rubbing is not carried out, the directions in which the liquidcrystalline molecules lying in gaps between the protrusions can berestricted to the azimuths of the liquid crystalline molecules incontact with the surfaces of the protrusions. When a voltage isincreased, the negative liquid crystalline molecules are tilted indirections vertical to the electric fields.

As mentioned above, the inclined surfaces fill the role of a trigger fordetermining azimuths in which the liquid crystalline molecules arealigned with application of a voltage. The inclined surfaces need nothave large area. With small inclined surfaces, when no voltage isapplied, the liquid crystalline molecules in almost all the regions ofthe liquid-crystal layer except the inclined surfaces are alignedvertically to the surfaces of the substrates. This results in nearlyperfect black display. Thus, a contrast can be raised.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more clearly understood from thedescription as set below with reference to the accompanying drawings,wherein:

FIGS. 1A and 1B are diagrams for explaining a panel structure and anoperational principle of a TN LCD;

FIGS. 2A to 2C are diagrams for explaining a change of viewing accordingto a change of viewing angle in the TN LCD;

FIGS. 3A to 3D are diagrams for explaining an IPS LCD;

FIG. 4 is a diagram giving a definition of a coordinate system employedin studying viewing of a liquid crystal display as an example of the IPSLCD;

FIG. 5 is a diagram showing a gray-scale reversal areas in the IPS LCD;

FIGS. 6A and 6B are diagrams showing examples of changes in displayluminance levels of display in relation to the polar angle;

FIGS. 7A to 7C are diagrams for explaining a VA LCD and problemsthereof;

FIGS. 8A to 8C are diagrams for explaining rubbing treatment;

FIGS. 9A to 9C are diagrams for explaining principles of the presentinvention;

FIGS. 10A to 10C are diagrams for explaining determination of anorientation by protrusions;

FIGS. 11A to 11C are diagrams showing examples of the protrusions;

FIGS. 12A to 12C are diagrams showing examples of realizing the domainregulating means;

FIG. 13 is a diagram showing overall configuration of a liquid crystalpanel of the first embodiment;

FIGS. 14A and 14B are diagrams showing the structure of a panel inaccordance with a first embodiment;

FIG. 15 is a diagram showing the relationship between a pattern ofprotrusions and pixels in the first embodiment;

FIG. 16 is a diagram showing the pattern of protrusions outside adisplay area of the first embodiment;

FIG. 17 is a sectional view of the LCD panel of the first embodiment;

FIGS. 18A and 18B are diagrams showing the position of a liquid-crystalinjection port of the LCD panel of the first embodiment;

FIG. 19 is a diagram showing contours of protrusions in a prototype ofthe first embodiment defined by performing measurement using a tracertype coating thickness meter;

FIGS. 20A and 20B are diagrams indicating a change in response speedaccording to a change of spacing between protrusions in the panel of thefirst embodiment;

FIG. 21 is a diagram indicating a change in switching speed according toa change of spacing between protrusions in the panel of the firstembodiment;

FIG. 22 is a diagram showing a viewing angle characteristic of the panelof the first embodiment;

FIGS. 23A to 23C are diagrams showing changes in display luminancelevels of the panel of the first embodiment;

FIGS. 24A and 24B are diagrams showing changes in display luminancelevels of the panel of the first embodiment;

FIG. 25 is a diagram showing a viewing angle characteristic of the panelof the first embodiment having a phase-difference film;

FIGS. 26A to 26C are diagrams showing changes in display luminancelevels of the panel of the first embodiment having a phase-differencefilm;

FIG. 27 is a diagram for explaining occurrence of light leakage near theprotrusions;

FIG. 28 is a diagram showing a change in transmittance according to achange of applied voltage;

FIG. 29 is a diagram showing a change in contrast ratio according to achange of applied voltage;

FIG. 30 is a diagram showing a change in transmittance of white displayaccording to a change of height of protrusions in the panel of the firstembodiment;

FIG. 31 is a diagram showing a change in transmittance of black displayaccording to a change of height of protrusions in the panel of the firstembodiment;

FIG. 32 is a diagram showing a change in contrast ratio according to achange of height of protrusions in the panel of the first embodiment;

FIG. 33 is a diagram showing a pattern of protrusions of the secondembodiment;

FIG. 34 is a diagram showing a pattern of protrusions of a thirdembodiment;

FIG. 35 is a diagram showing a modification of the pattern ofprotrusions of the third embodiment;

FIG. 36 is a diagram showing an alignment of liquid crystallinemolecules near apices of the protrusions;

FIGS. 37A and 37B are diagrams showing shapes of protrusions of a fourthembodiment; protrusions;

FIGS. 38A and 38B are diagrams showing a structure of a panel of a fifthembodiment;

FIG. 39 is a diagram showing a pattern of slits of a pixel electrode ofthe fifth embodiment;

FIG. 40 is a diagram showing an example of alignment of liquidcrystalline molecules at a connection of slits;

FIG. 41 is a diagram showing generations of domains in the panel of thefifth embodiment;

FIG. 42 is a diagram showing shapes of protrusions and slits of a sixthembodiment;

FIG. 43 is a diagram showing generations of domains at corners of theprotrusions and slits in the panel of the sixth embodiment;

FIG. 44 is a plan view of pixel portion in a LCD panel of the sixthembodiment;

FIG. 45 is a diagram showing a pattern of pixel electrodes of the sixthembodiment;

FIG. 46 is a sectional view of the LCD panel of the sixth embodiment;

FIG. 47 is a diagram showing a viewing angle characteristic of the panelof the sixth embodiment;

FIGS. 48A to 48C are diagrams showing changes in display luminancelevels of the panel of the sixth embodiment;

FIGS. 49A and 49B are diagrams showing a modification of pattern ofpixel electrodes of the sixth embodiment;

FIGS. 50A and 50B are diagrams showing a pattern of pixel electrodes anda structure of a panel of the seventh embodiment;

FIG. 51 is a plan view of pixel portion in a LCD panel of the seventhembodiment;

FIG. 52 is a diagram showing a structure of a panel of an eighthembodiment;

FIGS. 53A to 53J are diagrams showing a process for producing a TFTsubstrate of the eighth embodiment;

FIG. 54 is a diagram showing a pattern of protrusions a panel of a ninthembodiment;

FIG. 55 is a plan view of pixel portion in a LCD panel of the ninthembodiment;

FIG. 56 is a diagram showing a modification of pattern of protrusions ofthe ninth embodiment;

FIGS. 57A and 57B are diagrams for explaining influences of obliqueelectric fields at edges of an electrode;

FIG. 58 is a diagram for explaining a problem occurred in a structureusing zigzag protrusions;

FIG. 59 is a diagram showing in enlarged form the neighborhood of aportion where a schlieren structure is observed;

FIG. 60 is a diagram showing a region where response speed are reduced;

FIGS. 61A and 61B are sectional views of the portions where the responsespeed is reduced;

FIGS. 62A and 62B are diagrams showing a fundamental arrangement of aprotrusion with respect to an edge of pixel electrode in a tenthembodiment;

FIG. 63 is a diagram showing an arrangement of protrusions in the tenthembodiment;

FIG. 64 is a detailed diagram showing a distinctive portion of the tenthembodiment;

FIGS. 65A and 65B are diagrams for explaining a change in orientationdirection by irradiation of ultraviolet light;

FIG. 66 is a diagram showing a modification of the tenth embodiment;

FIGS. 67A to 67C are diagrams for explaining desirable arrangements ofthe protrusions and an edge of the pixel electrode;

FIG. 68 is a diagram for explaining desirable arrangements of thedepressions and an edge of the pixel electrode;

FIGS. 69A and 69B are diagrams showing desirable arrangements of theprotrusions and edges of the pixel electrode;

FIGS. 70A and 70B are diagrams showing a pattern of protrusions of aeleventh embodiment;

FIG. 71 is a diagram showing an example in which discontinuousprotrusions are provided in each pixel;

FIG. 72 is a diagram showing shapes of the pixel electrodes andprotrusions of a twelfth embodiment;

FIG. 73 is a diagram showing a modification of shapes of the pixelelectrodes and protrusions of a twelfth embodiment;

FIG. 74 is a diagram showing a modification of shapes of the pixelelectrodes and protrusions of a twelfth embodiment;

FIG. 75 is a diagram showing a pattern of protrusions of a thirteenthembodiment;

FIGS. 76A and 76B are sectional views of the third embodiment;

FIGS. 77A and 77B are diagrams showing an operation of a storagecapacitor (CS) and a structure of electrodes;

FIGS. 78A and 78B are diagrams showing an arrangement of protrusions andCS electrodes of a fourteenth embodiment;

FIGS. 79A and 79B are diagrams showing an arrangement of slits and CSelectrodes of a modification of the fourteenth embodiment;

FIGS. 80A and 80B are diagrams showing an arrangement of protrusions andCS electrodes of an another modification of the fourteenth embodiment;

FIGS. 81A and 81B are diagrams showing an arrangement of protrusions andCS electrodes of an another modification of the fourteenth embodiment;

FIG. 82 is a diagram showing a pattern of protrusions of the fifteenthembodiment;

FIGS. 83A to 83D are diagrams for explaining alignment changes of theliquid crystalline molecules in the fifteenth embodiment;

FIG. 84 is a diagram showing a viewing angle characteristic of the panelof the fifteenth embodiment;

FIGS. 85A to 85D are diagrams showing changes of response times betweengray-scale levels in the fifteenth embodiment, TN LCD, and other VALCDs;

FIGS. 86A and 86B are diagrams showing an arrangement of protrusions ofa modification of the fifteenth embodiment;

FIG. 87 is a diagram showing an arrangement of protrusions of anothermodification of the fifteenth embodiment;

FIG. 88 is a diagram showing an arrangement of protrusions of anothermodification of the fifteenth embodiment;

FIG. 89 is a diagram showing an arrangement of protrusions of anothermodification of the fifteenth embodiment;

FIGS. 90A and 90B are diagrams showing a structure of protrusions of asixteenth embodiment;

FIG. 91 is a diagram showing an arrangement of protrusions of thesixteenth embodiment;

FIGS. 92A and 92B are diagrams showing a structure of a panel of aseventeenth embodiment;

FIG. 93 is a diagram showing a structure of a panel of a eighteenthembodiment;

FIG. 94 is a diagram showing a structure of a panel of a nineteenthembodiment;

FIG. 95 is a diagram showing a structure of a panel of a twentiethembodiment;

FIG. 96 is a diagram showing a structure of a panel of a modification ofthe twentieth embodiment;

FIG. 97 is a diagram showing a structure of a panel of anothermodification of the twentieth embodiment;

FIG. 98 is a diagram showing a structure of a panel of anothermodification of the twentieth embodiment;

FIGS. 99A and 99B are diagrams showing a structure of a panel of a 21stembodiment;

FIGS. 100A and 100B are diagrams for explaining an influence of anassembly error to the alignment division;

FIGS. 101A and 101B are diagrams showing a structure of a panel of a22nd embodiment;

FIG. 102 is a diagram showing a structure of a panel of a 23rdembodiment;

FIGS. 103A and 103B are diagrams showing a structure of a panel of a24th embodiment;

FIG. 104 is a diagram showing a pattern of protrusions to which thestructure of the 24th embodiment is applied;

FIGS. 105A and 105B are diagrams showing a structure of a panel of a25th embodiment;

FIG. 106 is a diagram showing a structure of a panel in which arelationship of response time with respect to a gap length betweenprotrusions is measured;

FIG. 107 is a diagram showing the relationship of response time withrespect to the gap length;

FIGS. 108A and 108B are diagrams showing a relationship of atransmittance with respect to a gap between protrusions;

FIGS. 109A and 109B are diagrams showing an operational principle of the25th embodiment;

FIG. 110 is a diagram showing a structure of a panel of a 26thembodiment;

FIG. 111 is a diagram showing a viewing angle characteristic of thepanel of the 26th embodiment;

FIG. 112 is a diagram showing a pattern of protrusions of normal types;

FIG. 113 is a diagram showing wavelength dispersion characteristic ofthe optical anisotropy of the liquid crystal;

FIG. 114 is a diagram showing a pattern of protrusions of a 27thembodiment;

FIG. 115 is a diagram showing a relation between an applied voltage andtransmittance;

FIG. 116 is a diagram showing a pattern of protrusions of a 28thembodiment;

FIG. 117 is a diagram showing a pattern of protrusions of a 29thembodiment;

FIG. 118 is a diagram showing a pixel structure of the 29th embodiment;

FIG. 119 is a diagram showing shapes of protrusions of a 30thembodiment;

FIG. 120 is a diagram showing a change of transmittance according to achange of height of protrusions;

FIG. 121 is a diagram showing a change of a contrast ratio according toa change of height of protrusions;

FIG. 122 is a diagram showing a change of transmittance in white levelaccording to a change of height of protrusions;

FIG. 123 is a diagram showing a change of transmittance in black levelaccording to a change of height of protrusions;

FIGS. 124A and 124B are diagrams showing pixel structures of anmodification of the 30th embodiment;

FIGS. 125A and 125B are diagrams showing shapes of protrusions of a 31stembodiment;

FIG. 126 is a diagram showing a relationship between a twisted angle anda thickness of liquid crystal layer in a panel of the VA LCD;

FIG. 127 is a diagram showing a relationship between a relativeluminance of white level and a retardation of liquid crystal in thepanels of the VA LCD and TN LCD;

FIG. 128 is a diagram showing relationships between transmittances and aretardation of liquid crystal at respective wavelengths in the panel ofthe VA LCD;

FIG. 129 is a diagram showing relationships between response times and agap between protrusions at respective wavelengths in the panel of the VALCD;

FIG. 130 is a diagram showing relationships between an aperture ratioand a gap between protrusions at respective wavelengths in the panel ofthe VA LCD;

FIG. 131 is a diagram showing a structure of a panel of a 32ndembodiment;

FIG. 132 is a diagram showing a structure of a panel of a modificationof the 32nd embodiment;

FIG. 133 is a diagram showing a structure of a TFT substrate of a 33rdembodiment;

FIGS. 134A and 134B are diagrams showing a pattern of protrusions of the33rd embodiment;

FIG. 135 is a diagram showing a structure of a panel of a 34thembodiment;

FIGS. 136A and 136B are diagrams showing a pattern of protrusions of the34th embodiment;

FIGS. 137A to 137D are diagrams showing a process for producing a TFTsubstrate of the 35th embodiment;

FIG. 138 is a diagram showing a structure of a TFT substrate of the 35thembodiment;

FIGS. 139A to 139E are diagrams showing a process for producing a TFTsubstrate of the 36th embodiment;

FIGS. 140A and 140B are diagrams for explaining a problem of dielectricsubstance on an electrode;

FIGS. 141A and 141B are diagrams showing a structure of protrusions of a37th embodiment;

FIGS. 142A to 142E are diagrams showing a process for producingprotrusions of the 37th embodiment;

FIG. 143 is a diagram showing a structure of protrusions of a 38thembodiment;

FIGS. 144A and 144B are diagrams showing a change of a shape of aprotrusion due to baking;

FIGS. 145A to 145E are diagrams showing a change of the shape of theprotrusion according to baking temperatures;

FIGS. 146A to 146C are diagrams showing a change of the shape of theprotrusion according to a width of the protrusion;

FIGS. 147A and 147B are diagrams showing protrusions and a formingcondition of the vertical alignment film;

FIGS. 148A to 148C are diagrams showing an example of a method offorming protrusions according to a 39th embodiment;

FIGS. 149A and 148B are diagrams showing an another example of a methodof forming protrusions according to the 39th embodiment;

FIG. 150 is a diagram showing an another example of a method of formingprotrusions according to the 39th embodiment;

FIGS. 151A and 151B are diagrams showing changes of a repellentoccurrence ratio according to the ultraviolet light irradiation;

FIGS. 152A to 152C are diagrams showing an another example of a methodof forming protrusions according to the 39th embodiment;

FIGS. 153A to 153C are diagrams showing an another example of a methodof forming protrusions according to the 39th embodiment;

FIGS. 154A and 154B are diagrams showing an another example of a methodof forming protrusions according to the 39th embodiment;

FIGS. 155A and 155B are diagrams showing an another example of a methodof forming protrusions according to the 39th embodiment;

FIG. 156 is a diagram showing a temperature condition of the methodshown in FIGS. 155A and 155B;

FIGS. 157A to 157C are diagrams showing an another example of a methodof forming protrusions according to the 39th embodiment;

FIG. 158 is a diagram showing a structure of a panel of a prior artprovided with black matrices;

FIG. 159 is a diagram showing a structure of a panel of a 40thembodiment;

FIG. 160 is a diagram showing a pattern of protrusions of the 40thembodiment;

FIG. 161 is a diagram showing a shade pattern (black matrices) of a 41thembodiment;

FIG. 162 is a sectional view of a panel of the 41st embodiment;

FIG. 163 is a diagram showing pixels and a pattern of protrusions of a42nd embodiment;

FIG. 164 is a diagram showing a structure of a prior art panel havingspacers;

FIGS. 165A and 165B are diagrams showing structures of panels of a 43rdembodiment and an modification thereof;

FIGS. 166A and 166B are diagrams showing structures of panels ofmodifications of the 43rd embodiment;

FIG. 167 is a diagram showing a structure of a panel of a modificationof the 43rd embodiment;

FIGS. 168A to 168C are diagrams showing a process of a panel of a 44thembodiment;

FIG. 169 is a diagram showing a relationship between a scattered densityof spacers and a cell gap in the 44th embodiment;

FIG. 170 is a diagram showing a relationship between a scattered densityof spacers and generations of blemishes when a force is applied to thepanel;

FIGS. 171A and 171B are diagrams showing chemical formulas of crownadded to protrusion materials so that the protrusions have ionabsorption ability;

FIGS. 172A and 172B are diagrams showing chemical formulas of krypt andadded to protrusion materials so that the protrusions have ionabsorption ability;

FIGS. 173A and 173B are diagrams showing structures of CF substrates ofa 45th embodiment and a modification thereof;

FIG. 174 is a diagram showing a structure of a panel of a 46thembodiment;

FIGS. 175A and 175B are diagrams showing structures of CF substrates ofanother modifications of the 46th embodiment;

FIGS. 176A and 176B are diagrams showing structures of CF substrates ofanother modifications of the 46th embodiment;

FIGS. 177A and 177B are diagrams showing structures of CF substrates ofanother modifications of the 46th embodiment;

FIG. 178 is a diagram showing a structure of a panel of an anothermodification of the 46th embodiment;

FIGS. 179A and 179B are diagrams showing structures of CF substrates ofanother modifications of the 46th embodiment;

FIGS. 180A and 180B are diagrams showing structures of CF substrates ofanother modifications of the 46th embodiment;

FIGS. 181A to 181G are diagrams showing a process for formingprotrusions on the CF substrate according to a 47th embodiment;

FIG. 182 is a diagram showing a structure of a panel of the 47thembodiment;

FIGS. 183A and 180B are diagrams showing a process for forming blackmatrices of the CF substrate according to a 48th embodiment;

FIGS. 184A and 184B are diagrams showing a structure of a panel of the48th embodiment;

FIGS. 185A to 185C are diagrams showing a process for formingprotrusions on the CF substrate according to a 49th embodiment;

FIG. 186 is a diagram showing a structure of a panel of the 49thembodiment;

FIG. 187 is a diagram showing a process for forming protrusions on theCF substrate according to a 50th embodiment;

FIGS. 188A and 188B are diagrams showing a structure of a panel of the50th embodiment;

FIG. 189 is a diagram showing a structure of a CF substrate of a 51thembodiment;

FIGS. 190A and 190B are diagrams showing structures of CF substrates ofmodifications of the 51th embodiment;

FIG. 191 is a diagram showing structures of CF substrates ofmodifications of the 51th embodiment;

FIG. 192 is a diagram showing structures of CF substrates ofmodifications of the 51th embodiment;

FIG. 193 is a diagram showing a structure of a panel of an anothermodification of the 50th embodiment;

FIG. 194 is a diagram showing an example of a product employing the LCDin accordance with the present invention;

FIG. 195 is a diagram showing a structure of the product shown in FIG.197;

FIGS. 196A and 196B are diagrams showing examples of arrangements of theprotrusions in the product;

FIG. 197 is a flowchart showing a process of a panel according to thepresent invention;

FIG. 198 is a flowchart showing a process of forming protrusions;

FIG. 199 is a diagram for explaining a process of forming protrusions byprinting;

FIG. 200 is a diagram showing the configuration of a liquid-crystalinjection apparatus;

FIGS. 201A and 201B are diagrams showing examples of the positions ofliquid-crystal injection ports of the LCD panel;

FIGS. 202A and 202B are diagrams showing examples of the positions ofliquid-crystal injection ports of the LCD panel;

FIGS. 203A and 203B are diagrams showing examples of the positions ofliquid-crystal injection ports of the LCD panel;

FIG. 204 is a diagram showing a structure of electrodes near theliquid-crystal injection port in the panel of the present invention;

FIGS. 205A to 205C are diagrams for explaining a defect due tocontamination by polyurethane resin and skin in the VA LCD;

FIG. 206 is a diagram showing a relationship between a size ofpolyurethane resin particulate and a size of defective area;

FIG. 207 is a diagram showing a simulation result of a relationshipbetween a display frequency and an effective voltage at respectivespecific resistances;

FIG. 208 is a diagram showing a simulation result of a discharge time atrespective specific resistances;

FIG. 209 is a diagram showing a simulation result of a discharge time atrespective specific resistances;

FIG. 210 is a diagram showing a fundamental constitution of the priorart VA LCD;

FIG. 211 is a diagram showing a viewing angle characteristic (contrastratio) of the prior art VA LCD;

FIG. 212 is a diagram showing a viewing angle characteristic (gray-scalereversal) of the prior art VA LCD;

FIG. 213 is a diagram showing a fundamental constitution of the panel ofaccording to the present invention;

FIG. 214 is a diagram showing a viewing angle characteristic (contrastratio) of present invention;

FIG. 215 is a diagram showing a viewing angle characteristic (gray-scalereversal) of present invention;

FIG. 216 is a diagram for explaining characteristics of a retardationfilm;

FIG. 217 is a diagram showing a constitution of a panel of a 52ndembodiment;

FIG. 218 is a diagram showing a viewing angle characteristic (gray-scalereversal) of the 52nd embodiment;

FIG. 219 is a diagram showing a viewing angle characteristic (gray-scalereversal) of the 52nd embodiment;

FIG. 220 is a diagram showing a relationship of a polar angle at which apredetermined value of contrast can be obtained with respect to aretardation in the 52nd embodiment;

FIG. 221 is a diagram showing a constitution of a panel of a 53rdembodiment;

FIG. 222 is a diagram showing a viewing angle characteristic (gray-scalereversal) of the 52rd embodiment;

FIG. 223 is a diagram showing a viewing angle characteristic (gray-scalereversal) of the 52rd embodiment;

FIG. 224 is a diagram showing a relationship of a polar angle at which apredetermined value of contrast can be obtained with respect to aretardation in the 53rd embodiment;

FIG. 225 is a diagram showing a constitution of a panel of a 54thembodiment;

FIG. 226 is a diagram showing a relationship of a polar angle at which apredetermined value of contrast can be obtained with respect to aretardation in the 54th embodiment;

FIG. 227 is a diagram showing a change of an upper limit to the optimumcondition regarding contrast with respect to a retardation in the 54thembodiment;

FIG. 228 is a diagram showing a change of a polar angle at which nogray-scale reversal is generated with respect to a retardation in the54th embodiment;

FIG. 229 is a diagram showing a change of an upper limit to the optimumcondition regarding gray-scale reversal with respect to a retardation inthe 54th embodiment;

FIG. 230 is a diagram showing a viewing angle characteristic (gray-scalereversal) of the 55th embodiment;

FIG. 231 is a diagram showing a viewing angle characteristic (gray-scalereversal) of the 55th embodiment;

FIG. 232 is a diagram showing a constitution of a panel of a 56thembodiment;

FIG. 233 is a diagram showing a viewing angle characteristic (gray-scalereversal) of the 56th embodiment;

FIG. 234 is a diagram showing a viewing angle characteristic (gray-scalereversal) of the 56th embodiment;

FIG. 235 is a diagram showing a relationship of a polar angle at which apredetermined value of contrast can be obtained with respect to aretardation in the 56th embodiment;

FIG. 236 is a diagram showing a constitution of a panel of a 57thembodiment;

FIG. 237 is a diagram showing a viewing angle characteristic (gray-scalereversal) of the 57th embodiment;

FIG. 238 is a diagram showing a viewing angle characteristic (gray-scalereversal) of the 57th embodiment;

FIG. 239 is a diagram showing a relationship of a polar angle at which apredetermined value of contrast can be obtained with respect to aretardation in the 57th embodiment;

FIG. 240 is a diagram showing a constitution of a panel of a 58thembodiment;

FIG. 241 is a diagram showing a viewing angle characteristic (gray-scalereversal) of the 58th embodiment;

FIG. 242 is a diagram showing a viewing angle characteristic (gray-scalereversal) of the 58th embodiment;

FIG. 243 is a diagram showing a relationship of a polar angle at which apredetermined value of contrast can be obtained with respect to aretardation in the 58th embodiment;

FIG. 244 is a diagram showing a constitution of a panel of a 59thembodiment;

FIG. 245 is a diagram showing a viewing angle characteristic (gray-scalereversal) of the 59th embodiment;

FIG. 246 is a diagram showing a viewing angle characteristic (gray-scalereversal) of the 59th embodiment;

FIG. 247 is a diagram showing a relationship of a polar angle at which apredetermined value of contrast can be obtained with respect to aretardation in the 59th embodiment;

FIG. 248 is a diagram showing a change of an upper limit to the optimumcondition regarding contrast with respect to a retardation in the 59thembodiment;

FIG. 249 is a diagram showing a viewing angle characteristic of a panelof the 32th embodiment;

FIG. 250 is a diagram showing a change of an ion density when an ionabsorption treatment is applied to the protrusions;

FIGS. 251A to 251D are diagrams showing a process of a method of a panelof a modification in the 51st embodiment;

FIGS. 252A and 252B are diagrams showing a pattern of protrusions and asectional structure of the panel of the second embodiment;

FIG. 253 is a diagram showing a pattern of protrusions of an anothermodification of the second embodiment;

FIGS. 254A and 254B are diagrams showing a pattern of protrusions and asectional structure of the panel of the sixteenth embodiment;

FIG. 255 is a detailed diagram showing a distinctive portion of amodification of the tenth embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Before proceeding to a detailed description of the preferred embodimentsof the present invention, a prior art liquid crystal display device willbe described to allow a clearer understanding of the differences betweenthe present invention and the prior art.

FIGS. 1A and 1B are diagrams for explaining the structure and principlesof operation of a panel of the TN LCD. As shown in FIGS. 1A and 1B, analignment film is placed on transparent electrodes 12 and 13 formed onglass substrates, a rubbing treatment is performed so that orientationdirections of the liquid crystalline molecules on the two substrates areshifted by 90° to each other, and a TN liquid crystal is sandwichedbetween the transparent electrodes. Due to the properties of the liquidcrystal, liquid crystalline molecules in contact with the alignmentfilms are aligned in the directions of the orientation defined by thealignment films. The other liquid crystalline molecules are aligned inline with the aligned molecules. Consequently, as shown in FIG. 1A, theliquid crystalline molecules are aligned while twisted by 90°. Two sheetpolarizers 11 and 15 are located in parallel with the directions of theorientation defined by the alignment films.

When light 10 that is not polarized falls on a panel having theforegoing structure, the light passing through the sheet polarizer 11becomes linearly-polarized light and enters the liquid crystal. Sincethe liquid crystalline molecules are aligned while twisted 90°, theincident light is passed while twisted 90°. The light can therefore passthrough the lower sheet polarizer 15. This state is a bright state.

Next, as shown in FIG. 1B, when a voltage is applied to the electrodes12 and 13 and thus applied to the liquid crystalline molecules, theliquid crystalline molecules erect themselves to untwist. However, onthe surfaces of the alignment films, since an orientation control forceis stronger, the orientation of the liquid crystal remains matched withthe orientation defined by the alignment films. In this state, theliquid crystalline molecules are isotropic relative to passing light.The linearly-polarized light incident on the liquid-crystal layer willtherefore not turn the direction of polarization. The linearly-polarizedlight passing through the upper sheet polarizer 11 cannot therefore passthrough the lower sheet polarizer 15. This brings about a dark state.Thereafter, when a state in which no voltage is applied is resumed,display is returned to the bright state owing to the orientation controlforce.

The technology of manufacturing the TN TFT LCD has outstandinglyadvanced in recent years. Contrast and color reproducibility provided bythe TN TFT LCD have surpassed those offered by the CRT. However, the TNLCD has a critical drawback of a narrow viewing angle range. This posesa problem that the application of the TN LCD is limited. FIGS. 2A to 2Care diagrams for explaining this problem. FIG. 2A shows a state of whitedisplay in which no voltage is applied, FIG. 2B shows a state ofhalftone display in which an intermediate voltage is applied, and FIG.2C shows a state of black display in which a predetermined voltage isapplied. As shown in FIG. 2A, in the state in which no voltage isapplied, liquid crystalline molecules are aligned in the same directionwith a slight inclination (about 1° to 5°). In reality, the moleculesare twisted as shown in FIG. 1A. For convenience' sake, the moleculesare illustrated like FIG. 2A. In this state, light is seen nearly whitein any azimuth. Moreover, as shown in FIG. 2C, in the state in which avoltage is applied, intermediate liquid crystalline molecules exceptthose located near the alignment films are aligned in a verticaldirection. Incident linearly-polarized light is therefore seen black butnot twisted. At this time, light obliquely incident on a screen (panel)has the direction of polarization thereof twisted to some extent becauseit passes obliquely through the liquid crystalline molecules aligned inthe vertical direction. The light is therefore seen halftone (gray) butnot perfect black. As shown in FIG. 2B, in the state in which anintermediate voltage lower than the voltage applied in the state shownin FIG. 2C is applied, the liquid crystalline molecules near thealignment films are aligned in a horizontal direction but the liquidcrystalline molecules in the middle parts of cells erect themselveshalfway. The birefringent property of the liquid crystal is lost to someextent. This causes a transmittance to deteriorate and brings abouthalftone (gray) display. However, this refers only to light incidentperpendicularly on the liquid-crystal panel. Obliquely incident light isseen differently, that is, light is seen differently depending onwhether it is seen from the left or right side of the drawing. Asillustrated, the liquid crystalline molecules are aligned mutuallyparallel relative to light propagating from right below to left above.The liquid crystal hardly exerts a birefringent effect. Therefore, whenthe panel is seen from left, it is seen black. By contrast, the liquidcrystalline molecules are aligned vertically relative to lightpropagating from left below to right above. The liquid crystal exerts agreat birefringent effect relative to incident light, and the incidentlight is twisted. This results in nearly white display. Thus, the mostcritical drawback of the TN LCD is that the display state variesdepending on the viewing angle.

In an effort to solve the above problem, Japanese Examined PatentPublication (Kokai) Nos. 53-48452 and 1-120528 have proposed an LCDadopting a mode referred to as an IPS mode. FIGS. 3A to 3D are diagramsfor explaining the IPS LCD. FIG. 3A is a side view of the LCD with novoltage applied, FIG. 3B is a top view thereof with no voltage applied,FIG. 3C is a side view thereof with a voltage applied, and FIG. 3D is atop view with a voltage applied. In the IPS mode, as shown in FIGS. 3Ato 3D, slit-like electrodes 18 and 19 are formed in one substrate 17,and liquid crystalline molecules existent in a gap between the slit-likeelectrodes are driven with electric fields induced by a transverseelectric wave. A material exhibiting positive dielectric anisotropy isused to make a liquid crystal 14. When no electric field is applied, analignment film is rubbed in order to align the liquid crystallinemolecules homogeneously so that the major axes of the liquid crystallinemolecules will be nearly parallel to the longitudinal direction of theelectrodes 18 and 19. In the illustrated example, the liquidcrystalline-molecules are homogeneously aligned with an azimuth of 15°relative to the longitudinal direction of the slit-like electrodes inorder to make a direction (direction of turn), to which the orientationof the liquid crystal is changed with application of a voltage,constant. In this state, when a voltage is applied to the slit-likeelectrodes, as shown in FIG. 3C, liquid crystalline molecules existentnear the slit-like electrodes change their orientation so that the majoraxes thereof will be turned 90° relative to the longitudinal directionof the slit-like electrodes. However, since the other substrate 16 isorientationally processed so that liquid crystalline molecules will bealigned with an azimuth of 15° relative to the longitudinal direction ofthe slit-like electrodes, liquid crystalline molecules near thesubstrate 16 are aligned so that the major axes thereof will be nearlyparallel to the longitudinal direction of the electrodes 18 and 19. Theliquid crystalline molecules are therefore aligned while twisted fromthe upper substrate 16 to the lower substrate 17. In this kind of liquidcrystal display, when the sheet polarizers 11 and 15 are placed on andunder the substrates 16 and 17 respectively so that the axes oftransmission thereof will be orthogonal to each other. When the axis oftransmission of one sheet polarizer is made parallel to the major axesof the liquid crystalline molecules, black display can be attained withno voltage applied, and white display can be attained with a voltageapplied.

As mentioned above, the IPS mode is characterized in that the liquidcrystalline molecules do not erect themselves but turned in a transversedirection. In the TN mode or the like, when the liquid crystallinemolecules erect themselves, the birefringent property of the liquidcrystal varies depending on a direction of an viewing angle and aproblem occurs. When the liquid crystalline molecules are turned in thetransverse direction, the birefringent property hardly varies dependingon a direction. This results in very good viewing angle characteristics.However, the IPS mode has another problems. One of the problems is thata response speed is quite low. The reason why the response speed is lowis that although a gap between electrodes in the normal TN mode in whichliquid crystalline molecules are turned is 5 micrometers, the gap in theIPS mode is 10 micrometers or more. The response speed can be raised bynarrowing the gap between the electrodes. However, since electric fieldsof opposite polarities must be applied to the adjoining electrodes inthe IPS mode, when the gap between the electrodes is narrowed, a shortcircuit occurs to bring about a display defect. For this reason, the gapbetween the electrodes cannot be narrowed very much. Besides, when thegap between the electrodes is narrowed, the ratio in area of theelectrodes to display gets large. This poses a problem that atransmittance cannot be improved.

As mentioned above, the IPS mode suffers from slow switching. Atpresent, when a motion picture representing a fast motion is displayed,drawbacks including a drawback that an image streams take place. In anactual panel, therefore, for improving the response speed, as shown inFIGS. 3B and 3D, the alignment film is not rubbed parallel to theelectrodes but rubbed in a direction shifted by about 15°. For realizinghorizontal alignment, when an agent is merely applied to the alignmentfilm, liquid crystalline molecules are arrayed freely leftward orrightward and cannot be aligned in a predetermined direction. Rubbing istherefore carried out for rubbing the surface of the alignment film in acertain direction so that the liquid crystalline molecules will bealigned in the predetermined direction. When rubbing is carried out inthe IPS mode, if rubbing proceeds parallel to the electrodes, liquidcrystalline molecules near the center in the gap between the electrodesare slow to turn to the left or right with application of a voltage, andtherefore slow to respond to the application. Rubbing is therefore, asshown in FIGS. 3B and 3D, carried out in a direction shifted by about15° in order to demolish right-and-left uniformity. However, even whenthe direction of rubbing is thus shifted, since the response timepermitted by the IPS mode is twice longer than the one permitted by theTN mode, the response speed is very low. Moreover, when rubbing iscarried out in the direction shifted by about 15°, a viewing anglecharacteristic of a panel does not become uniform between the right andleft sides of the panel. Gray-scale reversal occurs relative to aspecified angle of a viewing angle range. This problem will be describedwith reference to FIGS. 4 to 6B.

FIG. 4 is a diagram giving a definition of a coordinate system employedin studying viewing of a liquid crystal display (of the IPS typeherein). As illustrated, a polar angle θ and azimuth φ are defined inrelation to substrates 16 and 17, electrodes 18 and 19, and a liquidcrystalline molecule 4. FIG. 5 is a diagram showing a gray-scalereversal characteristic of a panel concerning a viewing angle. A grayscale from white to black is segmented into 8 gray-scale levels. Domainareas causing gray-scale reversal when a change in luminance is examinedby varying the polar angle θ and azimuth φ are shown in FIG. 5. In thedrawing, reversal occurs at fours hatched areas. FIGS. 6A and 6B arediagrams showing examples of changes in luminance of display of 8gray-scale levels in relation to the polar angle θ with the azimuthsfixed to values of 75° and 135° causing reversal. White gray-scalereversal occurs at gray-scale levels associated with high luminances,that is, when white luminance deteriorates with an increasing value ofthe polar angle θ. Black gray-scale reversal occurs when black luminanceincreases with an increasing value of the polar angle θ. As mentioned,the IPS mode has a problem that gray-scale reversal occurs in fourazimuths. Furthermore, the IPS mode has a problem that it is harder tomanufacture the IPS LCD than the TN LCD. Thus, in the IPS mode, any ofthe other characteristics such as a transmittance, a response speed andproductivity, is sacrificed for the viewing angle characteristic.

As mentioned above, the IPS mode that has been proposed as analternative for solving the problem on the viewing angle characteristicof the TN mode has the problem that the characteristics offered by theIPS mode other than the viewing angle characteristic are insufficient. Avertically-aligned (VA) mode using a vertical alignment film has beenproposed. FIGS. 7A to 7C are diagrams for explaining the VA mode. The VAmode is a mode using a negative liquid crystal material and verticalalignment film. As shown in FIG. 7A, when no voltage is applied, liquidcrystalline molecules are aligned in a vertical direction and blackdisplay appears. As shown in FIG. 7C, when a predetermined voltage isapplied, the liquid crystalline molecules are aligned in a horizontaldirection and white display appears. A contrast in display offered bythe VA mode is higher than that offered by the TN mode. A response speedat black level is also higher. The VA mode is therefore attractingattention as a novel mode for a liquid crystal display.

However, the VA mode has the same problem as the TN mode concerninghalftone display, that is, a problem that the display state variesdepending on the viewing angle. For displaying a halftone in the VAmode, a voltage lower than a voltage to be applied for white display isapplied. In this case, as shown in FIG. 7B, liquid crystalline moleculesare aligned in an oblique direction. As illustrated, the liquidcrystalline molecules are aligned parallel to light propagating fromright below point to left above. The liquid crystal is therefore seenblack when viewed from the left side thereof because a birefringenteffect is hardly exerted on the left side thereof. By contrast, theliquid crystalline molecules are aligned vertically to light propagatingfrom left below to right above. The liquid crystal exerts a greatbirefringent effect relative to incident light, therefore, displaybecomes nearly white. Thus, there is the problem that the luminancevaries depending the viewing angle. The VA mode provides a much highercontrast than the TN mode and is superior to the TN mode in terms of aviewing angle characteristic, because even when no voltage is applied,liquid crystalline molecules near an alignment film are aligned nearlyvertically. However, the VA mode is not certainly superior to the IPSmode in terms of the viewing angle characteristic.

It is known that viewing angle performance of a liquid crystal displaydevice (LCD) in the TN mode can be improved by setting the orientationdirections of the liquid crystalline molecules inside pixels to aplurality of mutually different directions. Generally, the orientationdirection of the liquid crystalline molecules (pre-tilt angles) whichkeep contact with a substrate surface in the TN mode are restricted bythe direction of a rubbing treatment applied to the alignment film. Therubbing treatment is a processing which rubs the surface of thealignment film in one direction by a cloth such as rayon, and the liquidcrystalline molecules are orientated in the rubbing direction.Therefore, viewing angle performance can be improved by making therubbing direction different inside the pixels. FIGS. 8A to 8C show amethod of making the rubbing direction different inside the pixels. Asshown in this drawing, an alignment film 22 is formed on a glasssubstrate 16 (whose electrodes, etc., are omitted from the drawing).This alignment film 22 is then bought into contact with a rotatingrubbing roll 201 to execute the rubbing treatment in one direction.Next, a photo-resist is applied to the alignment film 22 and apredetermined pattern is exposed and developed by photolithography. As aresult, a layer 202 of the photo-resist which is patterned is formed asshown in the drawing. Next, the alignment film 22 is brought intocontact with a rubbing roll 201 that is rotating to the oppositedirection to the above so that only the open portions of the pattern arerubbed. In this way, a plurality of regions that are subjected to therubbing treatment in different directions are formed inside the pixel,and the orientation directions of the liquid crystal become pluralinside the pixel. Incidentally, the rubbing treatment can be done inarbitrarily different directions when the alignment film 22 is rotatedrelative to the rubbing roll 201.

Though the rubbing treatment has gained a wide application, it is thetreatment that rubbs and consequently, damages, the surface of thealignment film and involves the problem that dust is likely to occur.

A method which forms a concavo-convex pattern on an electrode is knownas another method of restricting the pre-tilt angle of the liquidcrystalline molecules in the TN mode. The liquid crystalline moleculesin the proximity of the electrodes are orientated along the surfacehaving the concavo-convex pattern.

FIGS. 9A to 9C are diagrams for explaining the principles of the presentinvention. According to the present invention, as shown in FIGS. 9A to9C, in the VA mode employing a conventional vertical alignment film andadopting a negative liquid crystal as a liquid crystal material, adomain regulating means is included for regulating the orientation of aliquid crystal in which liquid crystalline molecules are alignedobliquely when a voltage is applied so that the orientation will includea plurality of directions within each pixel. In FIGS. 9A to 9C, as thedomain regulating means, electrodes 12 on an upper substrate are slittedand associated with pixels, and an electrode 13 on a lower substrate isprovided with protrusions (projections) 20.

As shown in FIG. 9A, in a state in which no voltage is applied, liquidcrystalline molecules are aligned vertically to the surfaces of thesubstrates. When an intermediate voltage is applied, as shown in FIG.9B, electric fields oblique to the surfaces of the substrates areproduced near the slits of the electrodes (edges of the electrodes).Moreover, liquid crystalline molecules near the protrusions 20 slightlytilt relative to their state attained with no voltage applied. Theinclined surfaces of the protrusions and the oblique electric fieldsdetermine the directions in which the liquid crystalline molecules aretilted. The orientation of the liquid crystal is divided into differentdirections along a plane defined by each pair of protrusions 20 and thecenter of each slit. At this time, for example, light transmitted fromimmediately below to immediately above is affected by weak birefringencebecause the liquid crystalline molecules are slightly tilting.

Consequently, the transmission of light is suppressed and halftonedisplay of gray appears. Light transmitted from right above to leftbelow is hardly transmitted by a region of the liquid crystal in whichliquid crystalline molecules are tilting leftward, while the light isquite readily transmitted by a region thereof in which liquidcrystalline molecules are tilting rightward. On the average, halftonedisplay of gray appears. Light transmitted from left below to rightabove contributes to gray display due to the same principles.Consequently, homogeneous display can be attained in all azimuths.Furthermore, when a predetermined voltage is applied, liquid crystallinemolecules become nearly horizontal as shown in FIG. 9C. White displayappears. Thus, in all states of black display, halftone display, andwhite display, excellent display with little dependency on a viewingangle can be attained.

Now, FIGS. 10A and 10B are diagrams for explaining determination of anorientation by protrusions of dielectric material provided on theelectrodes. In the specification, the dielectric materials areinsulating materials of low dielectric. Referring to FIGS. 10A and 10B,an orientation determined by the protrusions will be discussed.

Protrusions are formed alternately on the electrodes 12 and 13, andcoated with the vertical alignment films 22: A liquid crystal employedis of a negative type. As shown in FIG. 10A, when no voltage is applied,the vertical alignment films 22 cause the liquid crystalline moleculesto align vertically to the surfaces of the substrates. In this case,rubbing need not be performed on the vertical alignment films. Liquidcrystalline molecules near the protrusions 20 try to align vertically tothe inclined surfaces of the protrusions. The liquid crystallinemolecules near the protrusions are therefore tilted. However, when novoltage is applied, in almost all regions of the liquid crystal otherthan the protrusions, liquid crystalline molecules are aligned nearlyvertically to the surfaces of the substrates. Consequently, as shown inFIG. 9A, excellent black display can appear.

When a voltage is applied, the distribution of electric potentials inthe liquid-crystal layer is as shown in FIG. 10B. In the regions of theliquid-crystal layer without the protrusions, the distribution isparallel to the substrates (electric fields are vertical to thesubstrates). However, the distribution is inclined near the protrusions.When a voltage is applied, as shown in FIGS. 7B and 7D, the liquidcrystalline molecules tilt according to an electric field strength.Since the electric fields are vertical to the substrates, when adirection of tilt is not defined by carrying out rubbing, the azimuth inwhich the liquid crystalline molecules tilt due to the electric fieldsincludes all directions of 360°. If there are pre-tilted liquidcrystalline molecules as shown in FIG. 10A, surrounding liquidcrystalline molecules are tilted in the directions of the pre-tiltedliquid crystalline molecules. Even when rubbing is not carried out, thedirections in which the liquid crystalline molecules lying in gapsbetween the protrusions can be restricted to the azimuths of the liquidcrystalline molecules in contact with the surfaces of the protrusions.As shown in FIG. 10B, the electric fields near the protrusions areinclined in directions in which they become parallel to the inclinedsurfaces of the protrusions. When a voltage is applied, the negativeliquid crystalline molecules are tilted in directions vertical to theelectric fields. The directions correspond to the directions in whichthe liquid crystalline molecules are pre-tilted because of theprotrusions. Thus, the liquid crystalline molecules are aligned on astabler basis. The slope of the protrusions and the electric fields inthe proximity of the inclined surfaces of the protrusions contribute tostable alignment. Furthermore, when a higher voltage is applied, theliquid crystalline molecules become nearly parallel to the substrates.

As mentioned above, the protrusions fill the role of a trigger fordetermining azimuths in which the liquid crystalline molecules arealigned with application of a voltage. The protrusions need not haveinclined surfaces (slopes) of large area. For example, the inclinedsurfaces over the whole pixel are unnecessary. However, if the size ofthe inclined surfaces is too small, the effect of the slope and electricfield are not available. Therefore, the width of the inclined surfacesare required to be determined according to the materials and shape ofthe protrusions. Because a good result is obtained when the width of theprotrusions is 5 μm. This means that when the width of the protrusionsis larger than 5 μm, a good result can be certainly obtained. With smallinclined surfaces, when no voltage is applied, the liquid crystallinemolecules in almost all the regions of the liquid-crystal layer exceptthe protrusions are aligned vertically to the surfaces of thesubstrates. This results in nearly perfect black display. Thus, acontrast ratio can be improved.

When the sections of the protrusions are rectangular, the side surfacesare almost vertical to the substrates. These side surfaces also operateas the domain regulating means. Therefore, the surfaces vertical to thesubstrates are included in the inclined surfaces.

The tilting direction of the orientation of the liquid crystal isdecided by domain regulating means. FIG. 11 shows the orientationdirection when protrusions are used as the domain regulating means. FIG.11A shows a bank having two slopes and the liquid crystalline moleculesare oriented in two directions different from each other at an angle of180 degrees with the bank being the boundary. FIG. 11B shows a pyramidand the liquid crystalline molecules are oriented in four directionsdifferent from one another at an angle of 90 degrees with the apex ofthe pyramid being the boundary. FIG. 11C shows a hemisphere and theorientation of the liquid crystalline molecules assumes symmetry ofrotation with the axis of the hemisphere perpendicular to the substratebeing the center. In the case of FIG. 11C, the display state becomes thesame for all the viewing angles. However, it cannot be said that alarger number of domains or directions is better. When the relationshipto the direction of polarization offered by a sheet polarizer is takeninto account, if the oblique orientation of the liquid crystal becomesrotationally symmetrical, there arises a problem that light useefficiency deteriorates. This is because when domains in the liquidcrystal are defined uninterruptedly and radially, liquid crystallinemolecules lying along a transmission axis and absorption axis of thesheet polarizer work inefficiently, and liquid crystalline moleculeslying in directions of 45° with respect to the axes work mostefficiently. For improving the light use efficiency, the directionsincluded in the oblique orientation of the liquid crystal are mainlyfour directions or less. When there are four directions, they shouldpreferably be directions in which light components to be projected onthe display surface of the liquid crystal display propagate withazimuths mutually different in increments of 90°. In this case, theratio in number of liquid crystalline molecules aligned in directions inwhich light components to be projected on the display surface propagatewith azimuth mutually different by 180° should preferably be nearlyeven. Out of two sets of liquid crystalline molecules aligned in thedirections in which the light components to be projected on the displaysurface propagate with azimuths mutually different by 180°, the ratio innumber of aligned liquid crystalline molecules of one set is nearlyeven, while the ratio in number of aligned liquid crystalline moleculesof the other set is uneven. The set of aligned liquid crystallinemolecules of which ratio in number is nearly even is a majority, and theset of aligned liquid crystalline molecules of which ratio in number isuneven may be negligible. In other words, a characteristic analogous tothat exhibited when two domains are defined in 180° different directionscan be realized.

In FIGS. 9A to 9C, for realizing the domain regulating means, theelectrodes 12 on the upper substrate are slitted and associated withpixels, and the electrode 13 on the lower substrate is provided with theprotrusions 20. Any other means will also do. FIGS. 12A to 12C arediagrams showing examples of realizing the domain regulating means. FIG.12A shows an example of realizing it by devising the shapes of theelectrodes, FIG. 12B shows an example of devising the contours of thesurfaces of the substrates, and FIG. 12C shows an example of devisingthe shapes of the electrodes and the contours of the surfaces of thesubstrates. In any of the examples, the orientations shown in FIG. 8 canbe attained. However, the structures of liquid crystals are a bitdifferent from one another.

In FIG. 12A, ITO electrodes 41 and 42 on both substrates or one of thesubstrates are slitted. The surfaces of the substrates are processed forvertical alignment, and a negative liquid crystal is sealed in. When novoltage is applied, liquid crystalline molecules are aligned verticallyto the surfaces of the substrates. When a voltage is applied, electricfields are generated obliquely to the surfaces of the substrates nearthe slits (edges) of the electrodes. With the oblique electric fields,the directions in which liquid crystalline molecules are tilted aredetermined. The orientation of the liquid crystal is divided asillustrated into right and left directions. In this example, the obliqueelectric fields induced near the edges of the electrodes are used toalign the liquid crystalline molecules rightward and leftward. Thistechnique shall therefore be referred to as an oblique electric fieldtechnique.

In FIG. 12B, protrusions 20 are formed on both the substrates. Like thestructure shown in FIG. 12A, the surfaces of the substrates areprocessed for vertical alignment, and a negative liquid crystal issealed in. When no voltage is applied, the liquid crystalline moleculesare aligned vertically to the surfaces of the substrates in principles.On the inclined surfaces of the protrusions, however, the liquidcrystalline molecules are aligned at a little tilt. When a voltage isapplied, the liquid crystalline molecules are aligned in the directionsof tilt. Moreover, when an insulating material with low dielectricconstant is used to form the protrusions, the electric fields areinterrupted (state close to the state attained by the oblique electricfield technique, the same state as the state attained by the structurehaving the electrodes slitted). More stable orientation division can beachieved. This technique shall be referred to as a both-side protrusiontechnique.

FIG. 12C shows an example of combining the techniques shown in FIGS. 12Aand 12B. The description will be omitted.

Three examples of realizing the domain regulating means have beenpresented. Moreover, various modifications can be devised. For example,the portions of the electrodes formed as the slits in FIG. 12A may bedented, and the dents may be provided with inclined surfaces. Instead ofmaking the protrusions in FIG. 12B using an insulating material,protrusions may be formed on the substrates, and ITO electrodes may beformed on the substrates and protrusions. Thus, the electrodes havingthe protrusions may be realized. Even this structure can regulate theorientation of the liquid crystal. Moreover, dents may be substitutedfor the protrusions. Furthermore, any of the described domain regulatingmeans may be formed on one of the substrates. When domain regulatingmeans are formed on both the substrates, any pair of domain regulatingmeans can be employed. Moreover, although the protrusions or dentsshould preferably be designed to have inclined surfaces, the protrusionsor dents having vertical surfaces can also exert an effect of a certainlevel.

When the protrusions are formed, during black display, parts of theliquid crystal lying in the gaps between the protrusions are seen black,but light leaks out through parts thereof near the protrusions. Thiskind of partial difference in display is microscopic and indiscernibleby naked eyes. The whole display exhibits averaged display intensity.The density for black display deteriorates a bit, whereby contrastdeteriorates. When the protrusions are made of a material not allowingpassage of visible light, contrast can be further improved.

When a domain regulating means is formed on one substrate or bothsubstrates, protrusions, dents, or slits can be formed like aunidirectional lattice with a predetermined pitch among them. In thiscase, when the protrusions, dents, or slits are a plurality ofprotrusions, dents, or slits bent at intervals of a predetermined cycle,orientation division can be achieved more stably. Moreover, when theprotrusions, dents, or slits are located on both substrates, they shouldpreferably be arranged to be offset by a half pitch.

In the constitution disclosed in Japanese Unexamined Patent Publication(Kokai) No. 6-301036, apertures (slits) are provided on only the counter(CF) substrate. Therefore, the size of domain areas cannot be too small.Contrarily, according to the present invention, the size of domain areascan be optionally determined because the domain regulating means areprovided on both of the pixel electrode and counter electrode. Further,at least one of the domain regulating means has inclined surfaces, theresponse speed can be improved.

On one of two upper and lower substrates, protrusions or dents may beformed like a two-dimensional lattice. On the other substrate,protrusions or dents may be arranged to be opposed to the centers ofsquares of the two-dimensional lattice.

In any case, it is required that orientation division occurs within eachpixel. The pitch of the protrusions, dents, or slits must be smallerthan that of pixels.

The results of examining the characteristics of an LCD in which thepresent invention is implemented demonstrate that a viewing anglecharacteristic is quite excellent and equal to or greater than those ofnot only a TN LCD but also an IPS LCD. Even when the LCD is viewed fromits front side, the viewing angle characteristic is quite excellent, andthe contrast ratio is 400 or more (twice as high as that offered by theTN LCD). The transmittance offered by the TN LCD is 30%, the one offeredby the IPS LCD is 20%, and the one offered by the present invention is25%. The transmittance offered by the present invention is lower thanthe one offered by the TN LCD but higher than the one offered by the IPSLCD. A response speed is outstandingly higher than those offered by theother modes. For example, as far as equivalent panels are concerned, aTN LCD panel exhibits an on speed (for transition from 0 V to 5 V) of 23ms, an off speed (for transition from 5 V to 0 V) of 21 ms, and aresponse speed (on+off) of 44 ms, while an IPS LCD panel exhibits an onspeed of 42 ms, an off speed of 22 ms, and a response speed of 64 ms.According to the mode of the present invention, the on speed is 9 ms,the off speed is 6 ms, and the response speed is 15 ms. Thus, theresponse speed is 2.8 times higher than the one offered by the TN modeand 4 times higher than the one offered by the IPS mode, and is a speedcausing no problem in display of a motion picture.

Furthermore, in the mode of the present invention, when no voltage isapplied, vertical alignment is achieved. When a voltage is applied,protrusions, dents, or oblique electric fields determine directions inwhich liquid crystalline molecules tilt. Unlike the ordinary TN or IPSmode, rubbing need not be carried out. In the process of manufacturing apanel, a rubbing step is a step likely to produce the largest amount ofrefuse. After the completion of rubbing, substrates must be cleaned(with running water or IPA) without fail. The cleaning may damage analignment film, causing imperfect alignment. By contrast, according tothe present invention, since the rubbing step is unnecessary, the stepof cleaning substrates is unnecessary.

FIG. 13 is a diagram showing the overall configuration of a liquidcrystal panel of the first embodiment of the present invention. As shownin FIG. 13, the liquid crystal panel of the first embodiment is a TFTLCD. A common electrode 12 is formed on one glass substrate 16. Theother glass substrate 17 is provided with a plurality of scan bus lines31 formed parallel to one another, a plurality of data bus lines 32formed parallel to one another vertically to the scan bus lines, andTFTs 33 and cell electrodes 13 formed like a matrix at intersectionsbetween the scan bus lines and data bus lines. The surfaces of thesubstrates are processed for vertical alignment. A negative liquidcrystal is sealed in between the two substrates. The glass substrate 16is referred to as a color filter (CF) substrate because color filtersare formed, while the glass substrate 17 is referred to as a TFTsubstrate. The details of the TFT LCD will be omitted. Now, the shapesof the electrodes which are constituent features of the presentinvention will be described.

FIGS. 14A and 14B are diagrams showing the structure of a panel inaccordance with the first embodiment of the present invention. FIG. 14Ais a diagram illustratively showing a state in which the panel is seenobliquely, and FIG. 14B is a side view of the panel. FIG. 15 is adiagram showing the relationship between a pattern of protrusions andpixels in the first embodiment, FIG. 16 is a diagram showing the patternof protrusions outside a display area of a liquid crystal panel of thefirst embodiment, and FIG. 17 is a sectional view of the liquid crystalpanel of the first embodiment.

As shown in FIG. 17, a black matrix layer 34, an ITO film 12 providingcolor filters and a common electrode, and protrusions 20 parallel to oneanother with an equal pitch among them are formed on the surface of aside of a CF substrate 16 facing a liquid crystal. The ITO film andprotrusions are coated with a vertical alignment film that is omittedtherein. Gate electrodes 31 forming gate bus lines, CS electrodes 35,insulating films 40 and 43, electrodes forming data bus lines, an ITOfilm 13 providing pixel electrodes, and protrusions parallel to oneanother with an equal pitch among them are formed on the surface of aside of a TFT substrate 17 facing the liquid crystal. The TFT substrateis further coated with a vertical alignment film, though the verticalalignment film is omitted from the figure. Reference numerals 41 and 42denote a source and drain of a TFT. In this embodiment, protrusions 20Aand 20B are made of a TFT flattening material (positive resist).

As shown in FIG. 14A, the pattern of the protrusions 20A and 20B is apattern of parallel protrusions extending straightly and arranged withan equal pitch among them. The protrusions 20A and 20B are arranged tobe offset by a half pitch. The structure shown in FIG. 14B is thusrealized. As mentioned in conjunction with FIG. 9B, the orientation ofthe liquid crystal is divided into two directions to thus divide eachdomain into two regions.

The relationship of the pattern of protrusions to pixels is shown inFIG. 15. As shown in FIG. 15, in a general color-display liquid crystaldisplay, three pixels of red, green, and blue constitute one colorpixel. The width of each of the red, green, and blue pixels isapproximately one-third of the length thereof so that color pixels canbe arrayed with the same gap kept above and below them. A pixel defineseach pixel electrode. Among arrayed pixel electrodes, gate bus lines(hidden behind the protrusions 20B) are laid down sideways, and data buslines 32 are laid down lengthwise. The TFTs 33 are located nearintersections between the gate bus lines 31 and data bus lines 32,whereby the pixel electrodes are interconnected. Opposed to the gate buslines 31, data bus lines 32, and TFTs 33 included in the respectivepixel electrodes 13 are black matrices 34 for intercepting light.Reference numeral 35 denotes CS electrodes used to provide a storagecapacitor for stabilizing display are placed. Since the CS electrodesare light-interceptive, the CS-electrode portions of the pixelelectrodes 13 do not work as pixels. Consequently, each pixel is dividedinto an upper part 13A and lower part 13B.

In each of the pixels 13A and 13B, three protrusions 20A are lying andfour protrusions 20B are lying. Three first regions each having theprotrusions 20B on the upper side of the panel and the protrusions 20Aon the lower side thereof, and three second regions each having theprotrusions 20A on the upper side thereof and the protrusions 20B on thelower side thereof are defined in one pixel composed of the pixels 13Aand 13B. In the pixel composed of the pixels 13A and 13B, a total of sixregions of the first and second regions are defined.

As shown in FIG. 16, on the margin of the liquid crystal panel, thepattern of the protrusions 20A and 20B is extending outside topmostpixels and beyond rightmost pixels. This is intended to alloworientation division to occur in the outermost pixels in the same manneras that in the inner pixels.

FIGS. 18A and 18B are diagrams showing the position of a liquid-crystalinjection port of the liquid crystal panel 100 of the first embodimentthrough which a liquid crystal is injected. As described later, in theprocess of assembling components to produce a liquid-crystal panel,after the CF substrate and TFT substrate are bonded to each other, aliquid crystal is injected. As far as a VA type TFT LCD is concerned, ittakes much time to inject a liquid crystal compared with the TN LCD ingeneral. Since protrusions are formed, it takes much more time to injecta liquid crystal. For shortening the time required for injecting theliquid crystal, as shown in FIG. 18A, a liquid-crystal injection port102 should preferably be formed on a side vertical to the direction inwhich the protrusions are arrayed parallel to one another on a cyclicbasis. Reference numeral 101 denotes a sealing line.

During injection of a liquid crystal, when the interior of the panel isdeaerated through exhaust ports 103 formed at another positions, theinternal pressure decreases. This makes it easy to inject a liquidcrystal. The exhaust ports should, as shown in FIG. 18B, be located on aside opposite to the side on which the injection port is located.

FIG. 19 shows contours of protrusions in a prototype defined byperforming measurement using a tracer type coating thickness meter. Asillustrated, the gap between the ITO electrodes 12 and 13 formed on thesubstrates is restricted to 3.5 micrometers by means of spacers 45. Theprotrusions 20A and 20B have a height of 1.5 micrometers and a width of5 micrometers. A pair of upper and lower protrusions 20A and 20B arespaced by 15 micrometers. This means that a spacing between adjoiningprotrusions formed on the same ITO electrodes is 35 micrometers.

After an intermediate voltage is applied to the panel of the secondembodiment, the interior of the panel is observed using a microscope.The observation has revealed that very stable alignment is attained.

Furthermore, in the panel of the first embodiment, a response speed hasquite improved. FIGS. 20A to 21 are diagrams indicating a changing valueof the response speed permitted by the panel of the first embodiment inrelation to changes in parameters that are an applied voltage and aspacing (gap) between upper and lower protrusions. FIG. 20A indicates anon speed (for transition from 0 to 5 V), FIG. 20B indicates an off speed(for transition from 5 to 0 V), and FIG. 21 indicates a switching speedthat is a sum of the on speed and off speed. As shown in FIGS. 20A to21, a fall time off is hardly dependent on the spacing but a rise timeon varies greatly. The smaller the spacing is, the higher the responsespeed becomes. Incidentally, the thickness of cells is 3.5 micrometers.The practical value of the spacing varies slightly depending thethickness of cells. That is to say, when the thickness of cells issmall, the spacing is widened. When the thickness of cells gets larger,the spacing is narrowed. It has been actually confirmed that as far asthe spacing is about 100 times larger than the thickness of cells,liquid crystalline molecules are aligned properly.

In any case, the panel of the first embodiment permits the satisfactoryswitching speed. For example, when the spacing between protrusions is 15micrometers and the thickness of cells is 3.5 micrometers, the responsespeed for transition between 0 and 5 V, that is, the on time on is 9 ms,the off time off is 6 ms, and the switching speed 15 ms. Thus, very fastswitching can be achieved.

FIGS. 22 to 24B are diagrams showing the viewing angle characteristic ofthe panel of the first embodiment. FIG. 22 two-dimensionally shows achange in contrast dependent on a viewing angle, and FIGS. 23A to 24Bshow changes in display luminance levels corresponding to 8 gray-scalelevels in relation to viewing angles. FIG. 23A shows a change occurringat an azimuth of 90°, FIG. 23B shows a change occurring at an azimuth of45°, and FIG. 23C shows a change occurring at an azimuth of 0°. FIG. 24Ashows a change occurring at an azimuth of −45°, and FIG. 24B shows achange occurring at an azimuth of −90°. Hatched parts of FIG. 22indicate areas in which a contrast is 10 or less, and double-hatchedparts thereof indicate areas in which the contrast is 5 or less. Asillustrated, a generally good characteristic is exhibited. However,since each pixel is divided vertically into two region, thecharacteristic is not a perfectly laterally and vertically uniformcharacteristic unlike the one provided by the first embodiment.Deterioration of contrast in a vertical direction is little larger thanthat in a lateral direction. The deterioration of contrast in thelateral direction is smaller than that in the vertical direction.However, as shown in FIG. 23C, gray-scale reversal of black occurs at aviewing angle of about 30°. Sheet polarizers are bonded in such a waythat the absorption axes thereof will lie at 45° and 135° respectivelywith respect to an optical axis. The viewing angle characteristic to beexhibited when the panel is viewed in an oblique direction is very good.The characteristics offered by this embodiment are overwhelminglysuperior to those offered by the TN mode. However, this embodiment isslightly inferior to the IPS mode in terms of viewing anglecharacteristic. However, once one phase-difference film or opticalcompensation film is placed on the panel of the first embodiment, theviewing angle characteristic of the panel can be improved so greatlythat it overwhelms the one offered by the IPS mode. FIGS. 25 to 26C arediagrams showing a viewing angle characteristic to be exhibited by thepanel of the first embodiment having the phase-difference film, andcorrespond to FIGS. 22 to 23C. As illustrated, deterioration of contrastdepending on a viewing angle has been drastically overcome. Moreover,gray-scale reversal occurring in a lateral direction on the panel hasbeen overcome. On the contrary, gray-scale reversal occurs in a verticaldirection during white display. However, generally, gray-scale reversalin white display is hardly visible to human eyes and is therefore notcounted as a problem in terms of display quality. Thus, once thephase-difference film is employed, better characteristics than thoseoffered by the IPS mode can be exhibited in all aspects including aviewing angle characteristic, response speed, and manufacturingdifficulty.

An attempt was made to discuss optimal conditions by creating variousvariations of the structure of the first embodiment or modifyingparameters other than the foregoing ones. In the case of protrusions,when the panel is displayed in black, light leaks out near theprotrusions. FIG. 27 is a diagram for explaining occurrence of lightleakage near the protrusions. As illustrated, light incident verticallyon portions of the electrodes 13 on the lower substrate on which theprotrusions 20 are formed is transmitted to some extent because liquidcrystalline molecules are as illustrated aligned obliquely along theinclined surfaces of the protrusions 20. This results in halftonedisplay. By contrast, liquid crystalline molecules near the apices ofthe protrusions are aligned in a vertical direction. No light thereforeleaks out near the apices. The same applies to the electrode 12 on theupper substrate. During black display, near the protrusions, halftonedisplay and black display are carried out partially. This partialdifference in display is microscopic and discernible to naked eyes. Thewhole display exhibits averaged display intensity. The black displaydeteriorates a bit, whereby contrast deteriorates. The protrusions aretherefore made of a material not allowing passage of visible light,namely, made of material shielding visible light, whereby contrastimproves. Even in the second embodiment, when the protrusions are madeof a material shielding visible light, contrast can be further improved.

A change in response speed occurring when the spacing betweenprotrusions is varied has been described in conjunction with FIGS. 20Ato 21. A change in characteristic deriving from a change in height ofprotrusions was measured. The width of a photo-resist to be applied forrealizing protrusions and the spacing between protrusions were 7.5micrometers and 15 micrometers respectively, and the thickness of cellswas approximately 3.5 micrometers. The height of the resist was set to1.537 μm, 1.600 μm, 2.3099 μm, and 2.4486 μm. The transmittance andcontrast ratio of a prototype were measured. The results of themeasurement are shown in FIGS. 28 and 29. A change in transmittancedependent on the height of the protrusions (resist) occurring in a whitestate (when 5 V is applied) is shown in FIG. 30. A change intransmittance dependent on the height of the protrusions (resist)occurring in a black state (when no voltage is applied) is shown in FIG.31. A change in contrast ratio dependent on the height of theprotrusions (resist) is shown in FIG. 32. The higher the resist is, thehigher the transmittance in the white state (when a voltage is applied)becomes. This is presumably attributable to the fact that theprotrusions (resist) filling a supplementary role for tilting liquidcrystalline molecules are large enough to turn down the liquidcrystalline molecules in terms of both of figures and electricaleffects. The transmittance (light leakage) in the black state (when novoltage is applied) increases with an increase in height of the resist.This causes black levels to fall and is therefore not very preferable.The causes of light leakage will be described in conjunction with FIG.27. Liquid crystalline molecules lying immediately above the protrusions(resist) and in the spacings between the protrusions are alignedvertically to the surfaces of the substrates. Light leakage does notoccur in these places. However, liquid crystalline molecules lying onthe slopes of the protrusions are aligned slightly obliquely. As theprotrusions get higher, the area of the slopes increases and a lightleakage increases.

The contrast (white luminance level/black luminance level) decreases asthe resist gets higher. However, even when the height of the resist isincreased to have the same value as the thickness of cells, screendisplay can be achieved without any problem. In this case, as describedlater, the protrusions (resist) can be designed to fill the role ofpanel spacers.

Based on the above results, prototypes of liquid crystal displays ofsize 15 were produced using TFT substrates and CF substrates havingprotrusions of 0.7 micrometers, 1.1 micrometers, 1.5 micrometers, and2.0 micrometers in height. The trend revealed by the results of theexperiment was also observed in the actually-produced liquid crystalpanels. For actual viewing, because the contrast has been originallyhigh, deteriorations in contrast occurring in the panels produced underthe different conditions were of a good level. Thus, satisfactorydisplay was achieved. This is presumably because the panels originallypermitted high contrasts and a little decrease in contrast wasindiscernible to human eyes. Moreover, a panel including protrusions of0.7 micrometers high was also produced in an effort to detect the lowerlimit of the height of the protrusions working on molecular alignment.Display was perfectly normal. Consequently, even when the height of theprotrusions (resist) is as small as 0.7 micrometers or less, theprotrusions can satisfactorily work on alignment of liquid crystallinemolecules.

FIG. 33 is a diagram showing a pattern of protrusions in the secondembodiment. As shown in FIG. 15, in the first embodiment, protrusionsare linear and extending in a direction vertical to the longer sides ofpixels. In the second embodiment, protrusions are extending in adirection vertical to the shorter sides of pixels 9. The othercomponents of the second embodiment are identical to those of the firstembodiment.

FIGS. 252A and 252B show a modification of the second embodiment,wherein FIG. 252A shows a protrusion pattern and FIG. 252B is asectional view showing the arrangement of the protrusion arrangement. Inthis modification, the protrusion 20A disposed on the electrode 12 onthe side of the CF substrate 16 is extended in such a fashion as to passthrough the center of the pixel 9 and to extend in a directionperpendicular to the minor side of the pixel 9. No protrusion isdisposed on the side of the TFT substrate 17. Therefore, the liquidcrystal is oriented in two directions inside each pixel. As shown inFIG. 252B, the domain is divided by the protrusion 20A at the center ofthe pixel. Since the edge of the pixel electrode serves as the domainregulating means around the pixel electrode 13, the orientation can bedivided stably. In this modification, only one protrusion is disposedfor each pixel and the distance between the protrusion 20A and the edgeof the pixel electrode 13 is great. Therefore, the response speedbecomes lower than in the second embodiment but the production processbecomes simpler because the protrusion is disposed on only one of thesides of the substrate. Further, because the occupying area of theprotrusion inside the pixel is small, display luminance can be improved.

FIG. 253 shows a protrusion pattern of another modification of thesecond embodiment. The protrusion 20A disposed on the electrode 12 onthe side of the CF substrate 16 is positioned at the center of the pixel9, and no protrusion is disposed on the side of the TFT substrate 17.The protrusion 20A is a pyramid, for example. Therefore, the liquidcrystal is oriented in four directions inside each pixel. Thismodification can obtain the same effect as that of the modificationshown in FIG. 255 and because the occupying area of the protrusioninside the pixel is further smaller, display luminance can be all themore improved.

In the first and second embodiments, numerous linear protrusionsextending unidirectionally are located parallel to one another.Orientation division caused by the protrusions divides each domainmainly into two regions. Azimuths with which liquid crystallinemolecules in two regions are aligned differ from each other by 180°. Theviewing angle characteristic for a halftone exhibited relative to lightcomponents propagating inside a panel with azimuths including an azimuthcorresponding to a direction in which liquid crystalline molecules arealigned vertically to the substrates will be improved as shown in FIGS.9A to 9C. As for the viewing angle characteristic exhibited relative tolight components propagating vertically to the light components, theproblem described in conjunction with FIGS. 7A to 7C occurs. For thisreason, orientation division should preferably be division of theorientation into four directions.

FIG. 34 is a diagram showing a pattern of protrusions in the thirdembodiment. As shown in FIG. 34, in the third embodiment, a pattern ofprotrusions extending lengthwise and a pattern of protrusions extendingsideways are created within each pixel 9. Herein, the pattern ofprotrusions extending lengthwise is created in the upper half of onepixel, and the pattern of protrusions extending sideways is created inthe lower half thereof. In this case, the pattern of protrusionsextending lengthwise divides the orientation of the liquid crystalsideways into azimuths that are mutually different by 180°, that is,divides each pixel or domain sideways into two regions. The pattern ofprotrusions extending sideways divides the orientation of the liquidcrystal lengthwise into azimuths that are mutually different by 180°,that is, divides each pixel or domain lengthwise into two regions.Consequently, the orientation of the liquid crystal within one pixel 9is divided into four directions. Talking of the whole liquid crystalpanel, the viewing angle characteristics thereof relative to both thevertical direction and lateral direction are improved. In the thirdembodiment, the components other than the pattern of protrusions areidentical to those of the first embodiment.

FIG. 35 is a diagram showing a modification of the pattern ofprotrusions of the third embodiment. This modification is different fromthe third embodiment shown in FIG. 34 in a point that a pattern ofprotrusions extending lengthwise is created in the left half of eachpixel, and a pattern of protrusions extending sideways is created in theright half thereof. Even in this case, like the patterns of protrusionsshown in FIG. 34, the orientation of the liquid crystal is divided intofour directions within each pixel 9. The viewing angle characteristicsof the panel relative to both the vertical direction and lateraldirection are improved.

The first to third embodiments use protrusions as a domain regulatingmeans for realizing orientation division. As shown in FIG. 36, thealignment of liquid crystalline molecules near the apices of theprotrusions is not regulated at all. Near the apices of the protrusions,the alignment of liquid crystalline molecules is therefore notcontrolled to deteriorate display quality. The fourth embodiment is anexample for solving this kind of problem.

FIGS. 37A and 37B are diagrams showing the shapes of protrusions in thefourth embodiment. The other components are identical to those of thefirst to third embodiments. In the fourth embodiment, as shown in FIG.37A, the protrusions 20 are partly tapered. The length of the taperportions is about 50 micrometers or less than it. For creating a patternof this kind of protrusions, the pattern is drawn using a positiveresist, and the protrusions and taper portions are created by performingslight etching. With the thus created protrusions, the alignment ofliquid crystalline molecules near the apices of the protrusions can becontrolled.

Moreover, in a modification of the fourth embodiment, as shown in FIG.37B, tapered juts 46 are formed on each protrusion 20. Even in thiscase, the length of each tapered portion is about 50 micrometers or lessthan it. For creating a pattern of this kind of protrusions, the patternis drawn using a positive resist, and the protrusions 20 are created byperforming slight etching. A positive resist whose thickness is about ahalf of the height of the protrusions is applied, and the tapered juts46 on the protrusions 2 are left intact by performing slight etching.With the juts, the alignment of liquid crystalline molecules near theapices of the juts can be controlled.

FIGS. 38A and 38B are diagrams showing the structure of a panel in thefifth embodiment. FIG. 38A is a diagram illustratively showing a statein which the panel is seen obliquely, and FIG. 38B is a side view. Thefifth embodiment is an example in which the structure of a panelcorresponds to the structure shown in FIG. 12C. The protrusions 20A arecreated as illustrated on the electrode 12 (herein, a common electrode)formed on the surface of one substrate by applying a positive resist,and the slits 21 are created in the electrodes 13 (herein, cell (pixel)electrodes) formed on the surface of the other substrate.

Cost serves as an important factor for determining whether a liquidcrystal display device could become commercially successful or not. Theliquid crystal display device of the VA system and, particularly, the VAsystem equipped with a domain regulating means features a high displayquality as described above but becomes expensive due to the provision ofthe domain regulating means and, hence, it has been desired to furtherdecrease the cost.

When the protrusion is formed on the electrode, the photoresist that isapplied must be exposed to light through a pattern followed bydeveloping and etching, requiring an increased number of steps andincreased cost, deteriorating the yield. On the other hand, the pixelelectrode must be formed by patterning, and the number of the steps doesnot increase despite a pixel electrode having a slit is formed. On theside of the TFT substrate, therefore, the cost can be decreased when thedomain regulating means is formed by slits rather than protrusions. Onthe other hand, the opposing electrode of the color filter substrate (CFsubstrate) is usually a flat electrode. When a slit is to be formed inthe opposing electrode, an etching step must be executed after thepatterned photoresist is developed. When the protrusion is to be formedon the opposing electrode, however, the developed photoresist can beused in its form without much driving up the cost of forming theprotrusion. Like in the liquid crystal display device of the firstembodiment of the present invention, therefore, the domain regulatingmeans on the side of the TFT substrate is formed by a slit in the pixelelectrode and the domain regulating means on the side of the colorfilter substrate is formed by a protrusion, driving up the cost little.

FIG. 39 is a diagram showing a pattern of slits of each pixel electrodein a modification of the fifth embodiment. This modification correspondsto an example in which the protrusions 20B are replaced with the slits21 in the third embodiment.

When a slit is formed in the pixel electrode to divide it into aplurality of partial electrodes, the same signal voltage must be appliedto these partial electrodes, and electric connection portions must beprovided to connect the partial electrodes together. When the electricconnection portions are formed on the same layer as the pixelelectrodes, orientation of liquid crystals is disturbed in the electricconnection portions impairing viewing angle characteristics, luminanceof the panel and response speed.

According to this as shown in FIG. 39, therefore, the electricconnection portions are formed in the perimeter of the pixel electrode13 and are shielded by the black matrices (BM) 34 to obtain luminanceand response speed comparable with those of when protrusions are formedon both of them. In this embodiment in which the CS electrode 35 havinglight-shielding property is provided at the central portion of thepixel, the pixel is divided into upper and lower two portions. Referencenumeral 34A denotes an opening of the upper side defined by BM, and 34Bdenotes an opening of the lower side defined by BM, and light passesthrough the inside of the openings.

The bus lines such as gate bus lines 31 and data bus lines 32 are madeof a metal material and have light-shielding property. To obtain stabledisplay, the pixel electrodes must be so formed as will not besuperposed on the bus lines, and light must be shielded between thepixel electrodes and the bus lines. Furthermore, when amorphous siliconis used as operation semiconductor, the element characteristics undergoa change upon the incidence of light giving rise to the occurrence oferroneous operation. Therefore, the TFT portions must be shielded fromlight. Therefore, the BM 34 has heretofore been provided for shieldinglight for these portions. According to this embodiment, the electricconnection portions are provided in the perimeter of the pixel, andlight is shielded by the BM 34. There is no need to newly provide the BMfor shielding light for the electric connection portions; i.e., theconventional BM may be used or the BM may be slightly expanded withoutdecreasing the numerical aperture to a serious degree.

The panel of the fifth embodiment is of a type in which each pixel isdivided into two portions, and therefore basically exhibits the samecharacteristics as the one of the first embodiment. The viewing anglecharacteristic of the panel becomes identical to that of the panel ofthe second embodiment when the phase-difference film or opticalcompensation film is employed. The response speed of the panel isslightly lower than that of the panel of the first embodiment, becauseoblique electric fields induced by the slits formed in one substratesare utilized. Nevertheless, the on speed is 8 ms, the off speed is 9 ms,and the switching speed is 17 ms. Thus, the response speed is muchhigher than the ones offered by the conventional modes. As mentionedabove, display is seen little irregular. However, the manufacturingprocess is simpler than those of the first and second embodiments. Forexample, in the course of forming ITO pixel electrodes (cell electrodes)on a TFT substrate, the electrodes are slitted. A pattern of protrusionsis then drawn on a common electrode using a photo-resist. As alreadydescribed, the rubbing step is unnecessary, and the associatedafter-rubbing cleaning step can therefore be omitted.

For the reference, the measurement results of an example in which slitsare provided on the cell (pixel) electrode and no slit is provided onthe counter electrode is described. In this example, the cell electrodeshave the slits, and the width and pitch of the slits are determinedproperly. Owing to this constitution, stable alignment is attained, thatis, liquid crystalline molecules are aligned in all azimuths of 360°inside walls defined with oblique electric fields induced near theslits. The liquid crystalline molecules are aligned in all azimuths of360° within each small region. The viewing angle characteristic of thepanel is therefore excellent. An image that is seen homogeneous in allazimuths of 360° can be produced. However, a response speed has not beenimproved. An on speed is 42 ms, and an off speed is 15 ms. A switchingspeed that is a sum of the on and off speeds is 57 ms. Thus, theresponse speed has not been improved very much. This means that noproblem occurs in displaying a still image but the response speed is nothigh enough to display a motion picture like the one offered by the IPSmode. If a number of the slits is decreased, the response speed isfurther decreased. This is presumably that when the number of the slitsis decreased, the area of each domain becomes large, and it lengthens atime in which all liquid crystalline molecules are oriented.

In the fifth embodiment, when a voltage is applied, the liquid crystalhas portions, in which molecular alignment is unstable. The reason willbe described with reference to FIGS. 40 and 41. FIG. 40 is a diagramillustrating the distribution of orientation of liquid crystallinemolecules in the electric connection portions. In a portion where theprotrusion 20A and the slit 21 are provided in parallel, the liquidcrystalline molecules are oriented in a direction perpendicular to thedirection in which the protrusion and the slit extend as viewed from theupper side. In the electric connection portion, however, the liquidcrystalline molecules 14 a are oriented in different directions,developing abnormal orientation. Therefore, as shown in FIG. 41, liquidcrystalline molecules in the spaces between the protrusions 20A and theslits 21 of the electrodes are aligned in a direction vertical (verticaldirection in the drawing) to the protrusions 20A and slits 21. Near theapices of the protrusions and the centers of the slits, liquidcrystalline molecules are aligned in a horizontal direction but not inthe vertical direction. Oblique electric fields induced by the slopes ofthe protrusions or the slits enable control of the liquid crystal in thevertical direction in the drawing but cannot enable control in thelateral direction. For this reason, a random domain is produced sidewaysnear the apices of the protrusions and the centers of the slits. Thishas been confirmed through microscopic observation. A domain near theapex of a protrusion is too small to be discerned, causing no problem.However, an area occupied by a domain having liquid crystallinemolecules aligned sideways and lying near a slit is so large as to bediscerned even by naked eyes. When the domain is produced regularly,even if the domain is large, it will not be cared. However, when thedomain is produced at random, an image is seen irregular. This leads todeteriorated display quality. The panel in the fifth embodiment makes alittle poor impression on image quality compared with the one providedby the first embodiment, though display has no problem.

Abnormal orientation causes the luminance of the panel and the responsespeed to decrease. For example, a comparison of a practical device inwhich an electric connection portion is formed at the central portion ofthe pixel electrode with a practical device in which a protrusion isprovided, indicates abnormal conditions such as a drop in the luminanceand a residual image in which white appears bright for a moment whenblack changes into white. In the sixth embodiment, this problem issolved.

A panel of the sixth embodiment is provided by modifying the shape ofthe protrusions 20A and that of the slits 21 in the cell electrodes 13in the panel of the fifth embodiment. FIG. 42 is a diagram showing theshape of the protrusions 20A of the sixth embodiment and that of thecell electrodes 13 thereof which are seen in a direction vertical to thepanel. As illustrated, the protrusions 20A are zigzagged. Owing to thisshape, as shown in FIG. 43, a domain divided regularly into four regionsis produced. Consequently, irregular display that poses a problem in thefifth embodiment can be overcome.

FIG. 44 is a plan view of a pixel portion in the LCD according to asixth embodiment of the present invention, FIG. 45 is a diagramillustrating a pattern of a pixel electrode according to the sixthembodiment, and FIG. 46 is a sectional view of a portion indicated byA-B in FIG. 44.

Referring to FIGS. 44 and 46, in the LCD of the sixth embodiment, on oneglass substrate 16 are formed a black matrix (BM) 34 for shielding lightand a color decomposition filter (color filter) 39, and a commonelectrode 12 is formed on one surface thereof. Moreover, sequences ofprotrusions 20A are formed in a zig-zag manner. The glass substrate 16on which the color filter 39 is formed is called color filter substrate(CF substrate). On the other glass substrate 17 are formed a pluralityof scan bus lines 31 arranged in parallel, a plurality of data bus lines32 arranged in parallel in a direction perpendicular to the scan buslines, TFTs 33 arranged like a matrix to correspond to the intersectingpoints of the scan bus lines and the data bus lines, and display pixel(cell) electrodes 13. The scan bus lines 31 form gate electrodes of theTFTs 33, and the data bus lines 32 form drain electrodes 42 of the TFTs33. The sources 41 are formed in the same layers as the data bus lines32 and are formed simultaneously with the formation of the drainelectrodes. A gate-insulating film, an amorphous silicon active layerand a channel protection film are formed on predetermined portionsbetween the scan bus line 31 and the data bus line 32, an insulatingfilm is formed on the layer of the data bus line 32 and, besides, an ITOfilm corresponding to the pixel electrode 13 is formed thereon. Thepixel electrode 13 is of a rectangular shape of 1:3 as shown in FIG. 45,and has a plurality of slits 21 in a direction tilted by 45 degrees withrespect to the sides thereof. In order to stabilize the potential ofevery pixel electrode 13, furthermore, a CS electrode 35 is provided toform a storage capacitor. The glass substrate 17 is called TFTsubstrate.

As shown, the sequences of protrusions 20A of the CF substrate and theslits 21 of the TFT substrates are arranged being deviated by one-halfpitch of their arrangement, so that the substrates maintain an inverserelationship. The protrusions and the slits maintain a positionalrelationship as shown in FIG. 12C, and the orientation of the liquidcrystals is divided into four directions. As described above, the pixelelectrode 13 is formed by forming an ITO film, applying a photoresistthereon, exposing it to light through a pattern of electrode, followedby developing and etching. Therefore, the slit can be formed through thesame step as the conventional step if the patterning is so effected asto remove the portion of the slit, without driving up the cost.

Upon forming the slits in the pixel electrode 13, the pixel electrode 13is divided into a plurality of partial electrodes. Here, however, asignal of the same voltage must be applied to the partial electrodesand, hence, the partial electrodes must be electrically connectedtogether. According to this embodiment as shown in FIG. 45, therefore,the pixel electrode 13 is not completely divided by slits, but theelectrode is left at the perimetric portions 131, 132, 133 of the pixelelectrode 13 to form electric connection portions. As described above,the alignments of the molecules are disturbed near the electricconnection portions. Therefore, according to this embodiment as shown inFIG. 10, the electric connection portions are formed in the perimeter ofthe pixel electrode 13 and are shielded by the BM 34 to obtain luminanceand response speed comparable with those of when protrusions are formedon both of them. In this embodiment in which the CS electrode 35 havinglight-shielding property is provided at the central portion of thepixel, the pixel is divided into upper and lower two portions. Referencenumeral 34A denotes an opening of the upper side defined by BM, and 34Bdenotes an opening of the lower side defined by BM, and light passesthrough the inside of the openings.

FIGS. 47 to 48C are diagrams showing a viewing angle characteristicexhibited by the sixth embodiment. As illustrated, the viewing anglecharacteristic is excellent and irregular display is overcome. Moreover,a response speed is as high as a switching speed is 17.7 ms. Thus, veryfast switching can be achieved.

FIGS. 49A and 49B illustrate another example of the pattern of the pixelelectrode, wherein the BM 34 shown in FIG. 49B is formed on the pixelelectrode 13 shown in FIG. 49A. The pattern of the pixel electrode canbe modified in a variety of ways. For example, electric connectionportions may be formed in the perimeter on both sides of the slit todecrease the resistance between the partial electrodes.

In the fifth and sixth embodiments, slits can be provided in the placeof the protrusions on the counter electrode 12. Namely, both of thedomain regulating means are realized by the slits. However, in thisconstitution, the response speed is decreased.

In the sixth embodiment, the electric connection portions are formed inthe same layer as the partial electrodes. The electric connectionportions, however, may be formed in a separate layer. A seventhembodiment deals with this case.

FIGS. 50A and 50B are diagrams illustrating a pattern and a structure ofthe pixel electrode according to the seventh embodiment. The seventhembodiment is the same as the sixth embodiment except that theconnection electrode 134 is formed simultaneously with the formation ofthe data bus line 32, and a contact hole is formed in the insulatinglayer 135 to connect the partial electrode 13 to the connectionelectrode 134. In this embodiment, the connection electrode 134 isformed simultaneously with the data bus line 32. However, the connectionelectrode 134 may be formed simultaneously with the gate bus line 31 orthe CS electrode 35. The connection electrode may be formed separatelyfrom the formation of the bus line. In this case, however, a step mustbe newly provided for forming the connection electrode, i.e., a new stepmust be added. In order to simplify the steps, it is desired to form theconnection electrode simultaneously with the formation of the bus lineor the CS electrode.

In the seventh embodiment, the connection electrode which becomes acause of abnormal orientation is more separated away from the liquidcrystal layer than that of the sixth embodiment, making it possible tofurther decrease abnormal orientation. When the connection electrode isformed of a light-shielding material, such a portion is shielded fromlight, and the quality of display is further improved.

FIG. 51 is a plan view of a pixel portion according to a eighthembodiment, and FIG. 52 is a sectional view of a portion A-B in FIG. 51.The eighth embodiment is the same as the sixth embodiment except that aprotrusion 20C is formed in the slit of the pixel electrode 13. Both theslit of the electrode and the insulating protrusion formed on theelectrode define the orientation region of the liquid crystals. When theprotrusion 20C is formed in the slit 21 as in this embodiment, thedirections of orientation of the liquid crystals due to the slit 21 andthe protrusion 20C are in agreement, the protrusion 20C assisting thedivision of orientation by the slit 21, to improve stability. Therefore,the orientation is more stabilized and the response speed is moreincreased than those of the first embodiment. Referring to FIG. 52, theprotrusion 20C is formed by laminating the layers that are formed whenthe CS electrode 35, gate bus line 31 and data bus line 32 are formed.

FIGS. 53A to 53J are diagrams illustrating a process for producing a TFTsubstrate according to the eighth embodiment. In FIG. 53A, a metal filmof the gate layer is formed on a glass substrate 17. In FIG. 53B,portions corresponding to gate bus lines 31, CS electrodes 35 andprotrusions 312 are left relying upon the photolithography method. InFIG. 53C, a gate-insulating film, an amorphous silicon active layer anda channel protection film are continuously formed. In FIG. 53D, thechannel protection film 314 is left in a self-aligned manner by exposureto light through the back surface. In FIG. 53E, a metal film 321 isformed for forming the contact layer and the source-drain layer. In FIG.53F, a source electrode 41 and a drain electrode 42 are formed relyingon the photolithography method. At this moment, the metal film is lefteven at a position corresponding to the protrusion 20C on the inside ofthe slit. In FIG. 53G, a passivation film 33 is formed. In FIG. 53H, acontact hole 332 is formed for the source electrode 41 and the pixelelectrode. In FIG. 53I, an ITO film 341 is formed. In FIG. 53J, a pixelelectrode 13 is formed by the photolithography method. Slits are formedat this moment.

According to this embodiment as described above, the protrusion 20C isformed in the slit 21 of the pixel electrode 13 without, however,increasing the number of the steps compared with the conventionalprocess. Besides, the orientation is further stabilized owing to theprotrusion 20C. In this embodiment, the protrusion in the slit of thepixel electrode is formed by superposing three layers, i.e., gate busline layer, channel protection layer and source/drain layer. Theprotrusion, however, may be formed by one layer or by a combination oftwo layers.

FIG. 54 is a diagram showing the shape of the protrusions 20A and 20B inthe ninth embodiment which are seen in a direction vertical to thepanel. FIG. 55 is a diagram showing a practical plan view of pixelportions of the ninth embodiment. A panel of the ninth embodiment of thepresent invention is provided by zigzagging the protrusions 20A and 20Bin the panel of the first embodiment like those in the one of the sixthembodiment. As illustrated, the protrusions 20A and 20B are zigzagged sothat an orientation causing each domain to be divided into four regionscan be attained. The directions of the surfaces of each protrusionreaching and receding from a bent are mutually different by 90°. Sinceliquid crystalline molecules are aligned in a direction vertical to thesurfaces of each protrusion, an orientation causing each domain to bedivided into four regions can be attained. In practice, a panel in whicha thickness of the liquid crystal layer is 4.1 μm, a width and height ofthe protrusions 20A are respectively 10 μm and 4 μm, a width and heightof the protrusions 20B are respectively 5 μm and 1.2 μm, a gap betweenthe protrusions 20A and 20B (a distance in the direction shifted by 45°from the horizontal line in the figure) is 27.5 μm, and a size of thepixel (pixel arrangement pitches) is 99 μm×297 μm has been made. As aresult of measurement of this panel, the response speed of the panel isidentical to that of the panel of the first embodiment. The viewingangle characteristic thereof is identical to the one in the sixthembodiment, and is so excellent as to demonstrate that the orientationis divided vertically and laterally uniformly. Optimal values of thewidth, height and gap of the protrusions have relations to each other.Further, they are changed according to materials of the protrusions,vertical alignment film, liquid crystal, a thickness of the liquidcrystal layer and so forth.

In the panel in the ninth embodiment, the direction of tilt of liquidcrystalline molecules can be controlled to include four directions.Regions A, B, C, and D in FIG. 54 are regions to be controlled so thatliquid crystalline molecules therein will be aligned in the fourdirections. The ratio of the regions within one pixel is uneven. This isbecause the pattern of protrusions is continuous and is located in thesame way in all pixels, and a pitch of repeated patterns of protrusionsis matched with a pitch of arrayed pixels. In reality, the viewing anglecharacteristic shown in FIG. 47 to 48C is exhibited but does not reflectthe uneven ratio of regions resulting from orientation division.However, this state is not very preferable. The pattern of protrusionsshown in FIG. 54 is therefore formed all over the substrates with thepitch of pixels ignored. The width of a resist is 7 micrometers, aninterval between resist lines is 15 micrometers, the height of theresist is 1.1 micrometers, and the thickness of cells is 3.5micrometers. Using a TFT substrate and CF substrate meeting theseconditions, a liquid crystal display of size 15 was produced as aprototype. Some resist lines interfered with gate bus lines and data buslines. Nevertheless, generally good display appeared. Even when thewidth of the resist was increased to be 15 micrometers and the intervalbetween resist lines was increased to 30 micrometers, nearly the sameresults were obtained. Consequently, when the width of protrusions andthe pitch of repeated patterns are made much smaller than the pitch ofpixels, even if a pattern of protrusions is drawn with the dimensions ofa pixel ignored, good display can be attained. Besides, the freedom indesign expands. For completely preventing interference with bus lines,the pitch of repeated patterns of protrusions or dents should be set toan integral submultiple or multiple of the pitch of pixels. Likewise, acycle of protrusions must be designed in consideration of a cycle ofpixels and should preferably be set to an integral submultiple ormultiple of the pitch of pixels.

In the ninth embodiment, when a pattern of protrusions that isdiscontinuous like the one shown in FIG. 56 is adopted, the ratio ofregions within one pixel in which liquid crystalline molecules arealigned in four different directions is even. There is still noparticular problem in manufacturing. However, since the pattern ofprotrusions is discontinuous, the orientation of the liquid crystal isdisordered at the edges of patterns. This leads to deteriorated displayquality such as light leakage. Even from this viewpoint, preferably, thepitch of repeated patterns of protrusions should be matched with thepitch of arrayed pixels, and a continuous pattern of protrusions shouldbe adopted.

In the ninth embodiment, the protrusions of dielectric materials areformed in a zig-zag manner on the electrodes 12, 13 as the domainregulating means and the protrusions regulate the alignment direction ofthe liquid crystalline molecules. As described above, the slits providedon the electrodes generate oblique electric fields, at the edgesthereof, and the oblique electric fields operate as the domainregulating means. The edges of the cell (pixel) electrodes also generateoblique electric field. Therefore, the oblique electric field must beconsidered as the domain regulating means.

FIGS. 57A and 57B are diagrams for explaining this phenomenon and showsthe case of the vertical orientation somewhat inclined from the verticaldirection. As shown in FIG. 57A, each liquid crystal particle 14 isoriented substantially vertically when no voltage is applied thereto.Upon application of a voltage between electrodes 12 and 13, however, anelectric field is generated in vertical direction in the electrodes 12and 13 in the region other than the perimeter of the electrode 13, sothat the liquid crystalline molecules 14 are tilted in the directionperpendicular to the electric field. One electrode is a commonelectrode, and the other electrode is a display pixel electrodeseparated into each display pixel. Therefore, as shown in FIG. 57B, thedirection of the electric field 8 is inclined at its perimetric edge(edge). The liquid crystalline molecules 14 are tilted in the directionperpendicular to the electric field 8. The direction of inclination ofthe liquid crystal, therefore, is different between the central portionand the edge of the pixel as shown. This phenomenon is called “reversetilt”. A reverse tilt causes a schlieren structure to be formed in thedisplay pixel area and thus deteriorates the display quality.

The reverse tilt also occurs in the case where the domain regulatingmeans is used. FIG. 58 is a diagram showing a portion 41 where theschlieren structure can be observed in a configuration formed with thezigzag protrusion pattern of the ninth embodiment. FIG. 59 is a diagramshowing in enlarged form the neighborhood of the portion 41 where aschlieren structure is observed and also shows the direction in whichthe liquid crystalline molecules 14 are tilted upon application of avoltage thereto. In this case, protrusions of different materials areformed on the pixel electrode substrate formed with a TFT and on theopposed substrate formed with a common electrode. A vertical alignmentfilm is printed, and the device is assembled without being rubbed. Thecell thickness is 3.5 μm. The portion 41 where the schlieren structureis observed is where the direction in which the liquid crystallinemolecules are fallen by the orientation regulation force due to thediagonal electric field is considerably different from the direction oforientation regulation due to the protrusions. This reduces the contrastand the response rate, thereby leading to a deteriorated displayquality.

In the case where the liquid crystal display device configured of aprotrusion pattern bent in zigzag in the ninth embodiment is driven, thedisplay is darkened in a part of the display pixels, or a phenomenoncalled an after-image in which a somewhat previous display appearsremaining occurs in the display of an animation or cursor relocation.FIG. 60 is a diagram showing a region appearing black in the pixel onthe liquid crystal panel configured in the ninth embodiment. In thisregion, the change in orientation is found to be very slow uponapplication of a voltage.

FIG. 61A is a sectional view taken in line A-A′ in FIG. 60, FIG. 61B isa sectional view taken in line B-B′. As shown in FIG. 60, the sectionA-A′ has a region looking black in the neighborhood of the left edge,while the neighborhood of the right edge lacks a region appearing black.In correspondence with this, as shown in FIG. 61A, the direction inwhich the liquid crystalline molecules are tilted by the orientationregulation force due to the diagonal electric field is considerablydifferent from the direction of orientation regulation due to theprotrusions in the neighborhood of the left edge, while the direction inwhich the liquid crystalline molecules are tilted by the orientationregulation force due to the diagonal electric field comparativelycoincides with the direction of orientation regulation due to theprotrusions in the neighborhood of the right edge. In similar fashion, aregion looking black is present in the neighborhood of the right edgebut absent in the neighborhood of the left edge. In correspondence withthis, as shown in FIG. 61B, the direction in which the liquidcrystalline molecules are tilted by the orientation regulation force dueto the diagonal electric field is considerably different from thedirection of orientation regulation due to the protrusions in theneighborhood of the right edge, while the direction in which the liquidcrystalline molecules are tilted by the orientation regulation force dueto the diagonal electric field comparatively coincides with thedirection of orientation regulation due to the protrusions in theneighborhood of the left edge.

As described above, the deterioration of the display quality isattributable to the portion where the direction in which the liquidcrystalline molecules are tilted by the orientation regulation force dueto the diagonal electric field at an edge of the display pixel electrodeis considerably different from the orientation regulation force due tothe protrusions upon application of a voltage thereto.

In the case where a liquid crystal display device having a configurationwith a protrusion pattern is driven, the display quality is seen todeteriorate in the neighborhood of the bus line (gate bus line or databus line) in the pixel. This is due to the undesirable minute region(domain) formed in the neighborhood of the bus line and the resultingdisturbance of liquid crystal orientation and reduced response rate. Theproblem thus is posed of a reduced viewing angle characteristic and areduced color characteristic in half tone.

FIGS. 62A and 62B are diagrams showing a fundamental configuration of aLCD according to a tenth embodiment. A pixel functions within the rangedefined by a cell electrode 13, which will be called a display regionand the remaining part a non-display region. Normally, a bus line and aTFT are arranged in a non-display region. A bus line made of a metalmaterial has a masking characteristic but a TFT transmits light. As aresult, a masking member called a black matrix (BM) is inserted betweena TFT, a cell electrode and a bus line.

According to the tenth embodiment, a protrusion 20A is arranged in thenon-display region on a common electrode 12 of a CF substrate 16 so asto generate an orientation regulation force in a direction differentfrom the orientation restriction force exerted due to a diagonalelectric field generated by an edge of the cell electrode 13. FIG. 62A,shows the state where no voltage is applied. In this state, liquidcrystalline molecules 14 are oriented substantially perpendicular to thesurfaces of the electrodes 12, 13 and the protrusion 20A due to thevertical orientation process. Upon application of a voltage thereto, asshown in FIG. 62B, the liquid crystalline molecules 14 are oriented inthe direction perpendicular to the electric field 8. In the non-displayregion lacking the cell electrode 13, the electric field is formeddiagonally from the neighborhood of an edge of the cell electrode 13toward the non-display region. This diagonal electric field tends toorient the liquid crystalline molecules 14 in a direction different fromthe orientation in the display region as shown in FIG. 57B. Theorientation regulation force of the protrusion 42, however, orients theliquid crystalline molecules 14 in the same direction as in the displayregion, as shown in FIG. 62A.

FIG. 63 is a diagram showing a protrusion arrangement pattern in aliquid crystal display device of the tenth embodiment. FIG. 64 is adiagram showing, in enlarged form, the portion defined by a circle inFIG. 63. In the tenth embodiment, a new protrusion 52 is formed in thevicinity of the portion where a shlieren structure is observed. Thisprotrusion 52 is connected to and integrally formed with a protrusionarrangement 20A formed on the common electrode 12. The relation shown inFIGS. 62A and 62B is realized at the portion formed with the protrusion52, where the orientation of the liquid crystalline molecules 14 at anedge of the cell electrode coincides with the orientation in the displayregion, as shown in FIG. 64. Therefore, the schlieren structure that hasbeen observed in FIG. 58 cannot be observed in FIG. 64 for an improvedisplay quality.

FIG. 255 shows a modification in which the protrusion 52 is arranged toface the edge of the pixel electrode 13. In this modification, noshlieren structure is observed.

The tenth embodiment, which uses an acrylic transparent resin for theprotrusion, can alternatively use a black material. The use of a blackresin material can shield the leakage light at the protrusion andtherefore improves the contrast. This is also the case with theembodiments described below.

The protrusion 52 which is formed as a non-display region domainregulating means in the non-display region as shown in FIGS. 62A to 63can be replaced by a depression (groove) with equal effect. Thedepression, however, is required to be formed on the TFT substrate.

Any non-display domain regulating means which has an appropriateorientation regulation force can be employed. The direction oforientation is known to change, for example, when the light of aspecific wavelength such as ultraviolet light is irradiated on thealignment film. Utilizing this phenomenon, it is possible to realize anon-display region domain regulating means by changing the direction oforientation in a part of the non-display region.

FIGS. 65A and 65B are diagrams for explaining the change in orientationdirection by irradiation of ultraviolet light. As shown in FIG. 65A, avertical alignment film is coated on the substrate surface, and anon-polarized ultraviolet light is irradiated on it from one directionat an angle of, say, 45° as shown in FIG. 65B. Then, the direction oforientation of the liquid crystalline molecules 14 is known to tilttoward the direction in which the ultraviolet light is irradiated.

FIG. 66 is a diagram showing a modification of the tenth embodiment. Theultraviolet light is irradiated from the direction indicated by arrow 54on a portion 53 of the alignment film on the TFT substrate opposed tothe protrusion 52 constituting the non-display domain regulating meansshown in FIG. 63. As a result, the portion 53 comes to have anorientation regulation force acting in such a direction as to offset theeffect of the diagonal electric field at the edge of the cell electrode13. Consequently, an effect similar to that of the tenth embodimentshown in FIG. 63 is obtained. The ultraviolet light, though irradiatedonly on the TFT substrate in FIG. 66, can alternatively be irradiatedonly on the CF substrate 16 or on both the TFT substrate and the CFsubstrate. The direction in which the ultraviolet light is irradiated isrequired to be set optimally striking a balance between the degree ofthe orientation regulation force in relation to the irradiationconditions and the orientation regulation force due to the diagonalelectric field.

The non-display region domain regulating means, which reduces the effectof the diagonal electric field generated at an edge of the cellelectrode on the orientation of the liquid crystalline molecules in thedisplay region and stabilizes the orientation of the liquid crystallinemolecules in the display region, is applicable to various systemsincluding the VA system.

Now, desirable arrangements of the protrusions and depressions, whichoperate as the domain regulating means, which respect to edges of pixelelectrodes will be described. FIGS. 67A to 67C are 22 diagrams showingfundamental relative positions of the edge of the cell electrode andprotrusions acting as domain regulating means. As shown in FIG. 67A,protrusions 20B are arranged at the edges of the cell electrode 13, or aprotrusion 20A is arranged on the common electrode 12 opposed to theedge of the cell electrode 13 as shown in FIG. 67B. As anotheralternative, the protrusion 20A on the CF substrate is formed inside thedisplay region with respect to the edges of the cell electrode 13, asshown in FIG. 67C, while the protrusion 20B on the TFT substrate 17 isarranged in the non-display region.

In FIGS. 67A and 67B, the protrusions are arranged at the edges of thecell electrode 13 or in opposed relation thereto, and the region wherethe protrusions affect the orientation direction of the liquid crystalis defined by the edges. Regardless of the state of the diagonalelectric field in the non-display region, therefore, the orientation inthe display region is not affected whatsoever. Thus, a stableorientation is secured in the display region and the display quality isimproved.

According to the conditions for arrangement shown in FIG. 67C, theorientation restriction force of the diagonal electric field at an edgeof the cell electrode 13 is in the same direction as the orientationregulation force of the protrusions, and therefore a stable orientationcan be obtained without developing any domain.

The conditions under which the direction of the orientation regulationforce of the diagonal electric field coincides with the direction of theorientation regulation force of the domain regulating means can berealized also using a depression instead of a protrusion. FIG. 68 is adiagram showing an arrangement of edges and depressions for realizingthe conditions for arrangement equivalent to FIG. 67C. Specifically, theprotrusions 20B on the TFT substrate 17 are arranged inside the displayregion, and the protrusions 20A on the CF substrate are arranged in thenon-display region with respect to the edges of the cell electrode 13.

FIGS. 69A and 69B are diagrams showing an arrangement of a linear(striped) protrusion arrangement constituting a domain regulating meanson a LCD realizing the conditions FIG. 67C in the first embodiment. FIG.69A is a top plan view and FIG. 69B is a sectional view. In theconfiguration of FIGS. 69A and 69B, the protrusion height is about 2 μm,the protrusion width is 7 μm and the inter-protrusion interval is 40 μm.After two substrates are attached to each other, the protrusions of theTFT substrate are arranged in a staggered fashion with the protrusionsof the CF substrate. In order to realize the conditions of FIG. 67C, theprotrusions of the TFT substrate 17 are interposed between the cellelectrodes 13. Since a gate bus line 31 is interposed between the cellelectrodes 13, however, the protrusion arranged between the cellelectrodes 13 is located on the gate bus line 31.

With the LCD of FIGS. 69A and 69B, no undesirable domain is observed andthe switching speed is not low at any portion. Therefore, a superiordisplay quality is obtained without any after-image. Assuming that theprotrusions 20B between the cell electrodes 13 in FIGS. 69A and 69B arearranged at the edges of the cell electrodes 13, the conditions of FIG.67A can be met, while if the arrangement of the protrusions 20A and 20Bis reversed between the two substrates, on the other hand, theconditions of FIG. 67B are satisfied. The protrusion arranged on or inopposed relation to the edges can alternatively be arranged either onthe TFT substrate 17 or on the CF substrate 16. Considering thedisplacement of the substrates attached to each other, however, theprotrusions are desirably formed at the edges of the cell electrodes 13on the TFT substrate 17.

FIGS. 70A and 70B are diagrams showing an arrangement of a protrusionarrangement of another protrusion pattern for a LCD according to aeleventh embodiment satisfying the conditions of FIG. 67C. FIG. 70A is atop plan view and FIG. 70B is a sectional view. As shown, a checkeredgrid of protrusions is arranged between the cell electrodes 13, andprotrusions similar in shape to the above-mentioned protrusion patternare formed sequentially inward of each pixel. By use of this protrusionpattern, the orientation in each pixel can be divided into fourdirections, but not in equal proportion. Also in this case, thecheckered protrusion pattern is arranged on the gate bus line 31 and thedata bus line 32 between the cell electrodes 13.

Also in FIGS. 70A and 70B, the conditions of FIGS. 67A and 67B aresatisfied if the protrusions 20B otherwise interposed between the cellelectrodes 13 are arranged at a portion in opposed relation to an edgeof the cell electrode 13 of the TFT substrate 17 or an edge of the CFsubstrate. In this case, too, the protrusions are preferably formed atthe edges of the cell electrode 13 on the TFT substrate 17.

In the example shown in FIGS. 70A and 70B, protrusions are formed inrectangular grid similar to the rectangular cell electrodes. Since theprotrusions are rectangular, however, an equal proportion cannot besecured for all the directions of orientation. In view of this, aprotrusion arrangement bent in zigzag shown in the ninth embodiment isconceived. As described with reference to FIGS. 58 and 60, however, anundesirable domain is generated in the neighborhood of the edges of thecell electrode 13 unless protrusions are formed as shown in FIG. 63. Forthis reason, independent protrusions for different pixels, not acontinuous arrangement of protrusions as shown in FIG. 71, is the nextsubject of discussion. In the case where the protrusions 20A and 20B areformed as shown in FIG. 71, however, an abnormal orientation occurs atthe portion indicated by T of the pixel 13, with the result that thedifference in distance from an electric field controller (TF) 33 posesthe problem of a reduced response rate. With the protrusion arrangementbent in zigzag in a rectangular pixel, it is impossible to satisfy theconditions for arrangement of the protrusions in relation to all theedges of the cell electrode shown in FIGS. 67A to 67C. A twelfthembodiment is intended to solve this problem.

FIG. 72 is a diagram showing the shapes of the cell electrode 13, thegate bus line 31, the data bus line 32, the TFT 33 and the protrusions20A, 20B according to the twelfth embodiment. As shown, in the twelfthembodiment, the cell electrode 13 has a shape similar to the bent formof the zigzag protrusions 20A, 20B. This shape prevents the occurrenceof an abnormal orientation, and the equal distance from the TFT 33 tothe end of the cell electrode 13 can improve the response rate.According to the twelfth embodiment, the gate bus line 31 is also bentin zigzag in conformance with the shape of the cell electrode 13.

As far as the protrusions arranged on the gate bus line 31 are formed onthe portions in opposed relation to the edges of the cell electrode 13or the edges of the CF substrate, the conditions of FIGS. 67A and 67Bare satisfied. In this case, too, the protrusions are desirably formedat the edges of the cell electrode 13 on the TFT substrate.

Nevertheless, the conditions of FIGS. 67A to 67C can be met only for theedges parallel to the gate bus line 31 but not for the edges parallel tothe data bus line 32. As a result, the latter portion is exposed to theeffect of the diagonal electric field, thereby posing the problemdescribed above with reference to FIGS. 57A to 60.

FIG. 73 is a diagram showing the shapes of the cell electrode 13, thegate bus line 31, the data bus line 32, the TFT 33 and the protrusions20A, 20B according to a modification of the twelfth embodiment. Unlikein the twelfth embodiment of FIG. 72 in which the gate bus line 31 isshaped in zigzag in conformance with the shape of the cell electrode 13,the cell electrode 13 is shaped as shown in FIG. 73, so that the gatebus line 31 is rectilinear while the data bus line 32 is bent in zigzag.In FIG. 73, the protrusions 20A and 20B are not independent fordifferent pixels but form a continuous protrusion covering a pluralityof pixels. The protrusion 20B is arranged on the data bus line 32 laidvertically between the cell electrodes 13 thereby to satisfy theconditions of 67C. The arrangement of FIG. 73 can also realize theconditions of FIGS. 67A and 67B, as far as the protrusions arranged onthe data bus line 32 are formed in spatially opposed relation to theedges of the cell electrode 13 or the edges of the CF substrate 16. Inthis case, too, the protrusions are desirably formed at the edges of thecell electrode 13 on the TFT substrate 17.

In the arrangement of FIG. 73, each protrusion crosses the edge of thecell electrode 13 parallel to the gate bus line 31. The resulting effectof the diagonal electric field on this portion gives rise to the problemdescribed above with reference to FIGS. 57A to 60.

FIG. 74 is a diagram showing another modification of the twelfthembodiment. In the arrangement shown in FIG. 74, the protrusions arebent twice in a pixel. This makes the pixel somewhat rectangular inshape as compared with FIG. 73 and therefore the display is easier toview.

FIG. 75 is a diagram showing the shapes of the cell electrode 13, thegate bus line 31, the data bus line 32, the TFT 33 and the protrusions20A, 20B according to a thirteenth embodiment. FIGS. 76A and 76B aresectional views taken in lines A-A′ and B-B′ in FIG. 75. In order toalleviate the effect of the diagonal electric field at the edges of thecell electrode 13 with a protrusion arrangement bent in zigzag, thetenth embodiment includes the non-display region domain regulating meansarranged outside the display region while the thirteenth embodiment hasthe cell electrode bent in zigzag, both having failed to completelyeliminate the effect of the diagonal electric field. In view of this,according to the thirteenth embodiment, the portion where theorientation is liable to be disturbed and an undesirable domain isliable to occur as shown in FIGS. 58 and 60 is masked by a black matrix34 to eliminate the effect of the diagonal electric field on thedisplay.

At the portion A-A′ shown in FIG. 75 is free of the effect of thediagonal electric field, the BM 34 is narrowed as shown in FIG. 76A,while at the portion B-B′ where the diagonal electric field has aconsiderable effect, the width of the BM 34 is increased as comparedwith the prior art so as not to display any image. In this way, thedisplay quality is not deteriorated nor an after-image or a reducedcontrast is caused. The increased area of the BM 34, however, reducesthe luminance of display due to a reduced numerical aperture.Nevertheless, no problem is posed as far as the area of the increase ofBM 34 is not considerable.

As described with reference to the tenth to thirteenth embodiments,according to this invention, the effect of the diagonal electric fieldat the edge portions of the cell electrode can be alleviated andtherefore the display quality can be improved.

In the embodiments as set above, the orientation of liquid crystal isdivided by the domain regulating means. A detailed observation of theorientation in the boundary portion of the domain, however, reveals thefact that the domain is divided in the directions 180° apart at thedomain regulating means, that minute domains 90° different in directionexist in the boundary portion (on a protrusion, a depression or a slit)between domains and that a region looking black exists in the boundary(the neighborhood of the edge of a protrusion, if any) of each domainincluding a minute domain. The region looking dark brings about areduced numerical aperture and darkens the display. As described above,the liquid crystal display device using a TFT requires a CS electrodecontributing to a reduced numerical aperture. In other cases, a blackmatrix (BM) is provided for shielding the surrounding of the displaypixel electrode and the TFT. In all of these cases, it is necessary toprevent the numerical aperture from being reduced as far as possible.

The use of a storage capacitor with the CS electrode was describedabove. Let us briefly explain the function of the storage capacitor (CS)and the electrode structure. The circuit of each pixel in a liquidcrystal panel having a storage capacitor is shown in FIG. 77A. As shownin FIG. 17, the CS electrode 35 is formed in parallel to the cellelectrode 13 in such a manner as to configure a capacitor elementbetween the CS electrode 35 and the cell electrode 13 through adielectric layer. The CS electrode 35 is connected to the same potentialas the common electrode 12, and therefore, as shown in FIG. 77A, astorage capacitor 2 is formed in parallel to the capacitor 1 due to theliquid crystal. Upon application of a voltage to the liquid crystal 1, avoltage is similarly applied to the storage capacitor 2, so that thevoltage held in the liquid crystal 1 is held also in the storagecapacitor 2. As compared with the liquid crystal 1, the storagecapacitor 2 is easily affected by a voltage change of the bus line orthe like, and therefore effectively contributes to suppressing anafter-image or a flicker and alleviating the display failure due to theTFT-off current. The CS electrode 35 is preferably formed in the samelayer as the gate (gate bus line), the source (data bus line) or thedrain (cell) electrode of the TFT element in order to simplify theprocess. Since these electrodes are formed of an opaque metal forsecuring the required accuracy, the CS electrode 35 is also opaque. Asdescribed above, the CS electrode is formed in parallel to the cellelectrode 13, and therefore the portion of the CS electrode cannot beused as a display pixel for a reduced numerical aperture.

The liquid crystal display device is required to have an improveddisplay luminance while an effort is being made to save powerconsumption at the same time. The numerical aperture, therefore, ispreferably as high as possible. As explained above, on the other hand,the light leakage through the slit formed in the protrusion or theelectrode for improving the display quality deteriorates the displayquality. For eliminating this inconvenience, the protrusion ispreferably made of a masking material and the slit is preferably maskedwith a BM or the like. Nevertheless, these measures contribute to alower numerical aperture.

An arrangement of the protrusions 20A, 20B and the CS electrode 35 ofthe embodiments as set above is shown in FIG. 77B. The protrusions 20A,20B and the CS electrode 35 are opaque to the light and thecorresponding portions have a lower numerical aperture. The protrusions20A, 20B are formed partly in superposition but partly not insuperposition on a part of the CS electrode 35.

FIGS. 78A and 78B are diagrams showing an arrangement of the protrusions20 (20A, 20B) and the CS electrodes 35 according to an 14th embodiment.FIG. 78A is a top plan view and FIG. 78B is a sectional view. As shown,a plurality of CS electrode units 35 are arranged under the protrusions20A, 20B. For a storage capacitor of a predetermined capacitance to berealized, a predetermined area is required of the CS electrode units 35.The combined area of the five units into which the CS electrode 35 isdivided as shown in FIGS. 78A and 78B coincides with the area of the CSelectrode 35 shown of FIGS. 77A and 77B. Further, in view of the factthat the CS electrode units and the protrusions 20A, 20B are allsuperposed one on another in FIGS. 78A and 78B, the numerical apertureis not substantially reduced more than it would be reduced by the CSelectrode alone. It follows, therefore, that the numerical aperture isnot reduced by the provision of the protrusions.

FIGS. 79A and 79B are diagrams showing an arrangement of the slits 21 ofthe electrodes 12, 13 and the CS electrode units 35 according to amodification of the 14th embodiment. FIG. 79A is a top plan view andFIG. 79B is a sectional view. The slits 21 function as a domainregulating means and are preferably masked for preventing the lightleakage therethrough. In this modification, the leakage light at theslits 21 is masked by the CS electrode units 35. Since the total area ofthe CS electrode units 35 remains the same, the numerical aperture isnot reduced.

FIGS. 80A and 80B are diagrams showing an arrangement of the slits 21 ofthe electrodes 12, 13, and the CS electrode units 35 according toanother modification of the 11th embodiment. FIG. 80A is a top plan viewand FIG. 80B is a sectional view. This modification is identical to theaforementioned modification of FIGS. 78A and 78B except that theprotrusions are bent in zigzag.

FIGS. 81A and 81B are diagrams showing an arrangement of the slits 21 ofthe electrodes 12, 13, and the CS electrode units 35 according toanother modification of the 14th embodiment. FIG. 81A is a top plan viewand FIG. 81B is a sectional view. This modification represents the casein which the total area of the protrusions 20A, 20B is larger than thetotal areas of the CS electrode units 35. According to thismodification, the CS electrode units are arranged at positionscorresponding to the edges of the protrusions 20A, 20B and not arrangedat the central portion of the protrusion. As a result, a minute domainhaving an orientation angle 90° different existing in the neighborhoodof the top of the protrusion can be effectively utilized for a brighterdisplay.

The constitution in which the CS electrode is divided into a pluralityof CS electrode unit can be adapted to a case in which the depressions(grooves) are used as the domain regulating means.

The 14th embodiment described above can prevent the reduction innumerical aperture which otherwise might be caused by the domainregulating means used.

FIG. 82 shows a protrusion pattern of the fifteenth embodiment. In thisfifteenth embodiment, linear protrusions 20A and 20B are disposed inparallel with one another on the upper and lower substrates,respectively, so that when they are viewed from the surface of thesubstrates, these protrusions 20A and 20B orthogonally cross oneanother. The liquid crystalline molecules 14 are orientedperpendicularly to the slopes under the state where no voltage isapplied between the electrodes but the liquid crystalline molecules inthe proximity of the slopes of the protrusions 20A and 20B are orientedperpendicularly to the slopes. Therefore, the liquid crystallinemolecules in the proximity of the slopes of the protrusions 20A and 20Bare inclined under this state and moreover, the directions ofinclination are different by 90 degrees near the protrusions 20A and20B. When the voltage is applied between the electrodes, the liquidcrystalline molecules are inclined in a direction which is parallel tothe substrates, but because the liquid crystalline molecules areregulated in the directions different by 90 degrees near the protrusions20A and 20B, respectively, they are twisted. The change of the image inthe case of twisting in this fifteenth embodiment is the same as that ofthe TN mode shown in FIGS. 2A to 2C. FIG. 2C shows the state when novoltage is applied and this is different only in that when the voltageis applied, the state becomes the one shown in FIG. 2A. As shown in FIG.82, further, four different twist regions are defined in the rangeencompassed by the protrusions 20A and 20B in the fifteenth embodiment.In consequence, viewing angle performance is excellent, too.Incidentally, the directions of the twists are different among theadjacent regions.

FIGS. 83A to 83D explanatory views useful for explaining why theresponse speed in the fifteenth embodiment is higher than that of thefirst embodiment. FIG. 83A shows the state where no voltage is applied,and the liquid crystalline molecules are oriented perpendicularly to thesubstrates. When the voltage is applied, the liquid crystallinemolecules are inclined in such a manner as to twist in the LCD of thefifteenth embodiment as shown in FIG. 83B. In contrast, the liquidcrystalline molecules at other portions are oriented by using the liquidcrystalline molecules keeping touch with the protrusions as the triggerin the LCD of the first embodiment as shown in FIG. 83C. However, theliquid crystalline molecules near the centers of the upper and lowerprotrusions move irregularly when the orientation changes because theyare not limited, and they are oriented in the same direction as shown inFIG. 83D after the passage of a certain period of time. Generally, thechange speed of the twist of the LCDs is high not only in the LCD of theVA system LCD using the protrusions, and the response speed of thefifteenth embodiment is higher than that of the first embodiment.

FIG. 84 shows viewing angle performance of the LCD of the fifteenthembodiment. This viewing angle performance is extremely excellent in thesame way as that of the VA LCD of the first embodiment, and is naturallyhigher than that of the TN mode and is at least equal to that of the IPSmode.

FIG. 85A is a diagram showing the response-speeds with the change of thegray-scale at the 16th graduation, 32nd gradation, 48th gradation, 64thgradation and black (first gradation) when 64-gradation display iseffected in the LCD of the fifteenth embodiment. For reference, FIG. 85Bshows the response speed of the TN mode, FIG. 85C shows the responsespeed of the mono-domain VA mode in which the orientation is not dividedand FIG. 85D shows the response speed of the multi-domain VA mode usingthe parallel protrusions of the first embodiment. For example, theresponse speed from the full black to the full white is 58 ms in the TNmode, 19 ms in the mono-domain VA mode and 19 ms in the multi-domainsystem, whereas it is 19 ms in the fifteenth embodiment, and this valueremains at the same level as those of other VA mode. The response speedfrom the full white to the full black is 21 ms in the TN mode 12 ms inthe mono-domain VA mode and 12 ms in the multi-domain type, whereas itis 6 ms in the fifteenth embodiment, and this value is higher than thoseof other VA modes. Further, the response speed from the full to the 16thgradation is 30 ms in the TN mode, 50 ms in the mono-domain type and 130ms in the multi-domain type, whereas it is 28 ms in the fifteenthembodiment, and this value remains at the same level as that of the TNmode and is by far more excellent than the values of other VA modes. Theresponse speed from the 16th gradation to the full black is 21 ms in theTN mode, 9 ms in the mono-domain type and 18 ms in the multi-domaintype, whereas it is 4 ms in the fifteenth embodiment and this value ismore excellent than the values of any other modes. Incidentally, theresponse speed of the IPS mode is extremely lower in comparison with anyother modes, and the response speeds from the full black to the fullwhite and vice versa are 75 ms, the response speed from the full blackto the 16th gradation is 200 ms and the response-speed from the 16gradation to the full black is 75 ms.

As described above, the LCD of the fifteenth embodiment are extremelyexcellent in both viewing angle performance and the response speed.

FIGS. 86A and 86B shows another protrusion patterns for accomplishingthe twist type VA system described above. In FIG. 86A protrusions 20Aand 20B are interruptedly disposed in such a fashion as to extendorthogonally in two directions on the respective substrates and not tocross one another, but to cross one another when they are viewed fromthe respective substrates. In this embodiment, four twist regions areformed in the different way from FIG. 82. The direction of the twist isthe same in each twist region but the rotating positions deviate fromone another by 90 degrees. In FIG. 86B protrusions 20A and 20B aredisposed in such a fashion as to extend orthogonally in two directionsto the respective substrates and to cross one another but to deviatemutually in both directions. In this embodiment, two twist regionshaving mutually different twist directions are formed.

In FIGS. 82, 86A and 86B, the protrusions 20A and 20B disposed on thetwo substrates need not be disposed in such a fashion as to orthogonallycross one another. FIG. 87 shows a modification wherein the protrusions20A and 20B shown in FIG. 82 are so disposed as to cross one another atan angle other than 90 degrees. In this case, too, four twist regionshaving mutually different twist directions are formed, and the quantityof the twist is different between the two opposed regions.

Furthermore, the same result can be obtained when slits are disposed inplace of the protrusions 20A and 20B shown in FIGS. 82, 86A and 86B.

In the fifteenth embodiment shown in FIG. 82, there is no means forcontrolling the orientation at the center portion in the frameencompassed by the protrusions 20A and 20B in comparison with theportions near the protrusions, and the orientation is likely to bedisturbed because it is far from the protrusions. For this reason, anelongated time is necessary before the orientation gets stabilized, andit is expected that the response speed at the center portion becomeslower. The response speed attains the highest at the corner portions ofthe frame because they are affected strongly by the protrusions servingas two adjacent sides. The influences of the orientation at the cornerportions are transferred to the center portion, impinge with theinfluences of other twist regions and the twist regions are rendereddefinite and are stabilized. In this way, all the liquid crystals arenot simultaneously oriented, but certain portions are first oriented andthen this orientation is transmitted to the portions nearby. Therefore,the response speed becomes slower at the center portion far from theprotrusions. When the frame defined by crossing is a square as shown inFIG. 82 for example, the influences are transferred from the fourcorners but when the frame defined by the crossing protrusions is theparallelogram as shown in FIG. 87, the influences are transferred fromthe acute angle portions, where the influences of the protrusions arestronger, to the center portion. The influences impinge at the centerportion and are further transferred to the corners having an obtuseangle. Therefore, the response speed becomes slower in theparallelogramic frame than in the square frame. To solve such a problem,a protrusion 20D similar to the frame is disposed at the center of eachframe as shown in FIG. 88. An excellent response speed can be obtainedwhen, for example, the protrusions 20A and 20B has a width of 5 μm and aheight of 1.5 μm, the gap of the protrusions is 25 μm and the protrusion20D is a square pyramid having a bottom of 5 μm.

FIG. 89 shows another embodiment wherein the protrusion is disposed atthe center of each frame of the protrusion pattern shown in FIG. 87. Thesame result as that of FIG. 82 can be obtained according to thisarrangement, too.

In the constructions shown in FIGS. 82, 86A, 86B and 87 wherein theprotrusions 20A and 20B cross one another, the thickness of the liquidcrystal layer can be limited at the portions at which the protrusions20A and 20B cross one another by setting the sum of the height of theprotrusions 20A and 20B to a value equal to the gap of the substrates,that is, the thickness of the liquid crystal layer. According to thisarrangement, the spacer need not be used. and 87 wherein the protrusions20A and 20B cross one another, the thickness of the liquid crystal layercan be limited at the portions at which the protrusions 20A and 20Bcross one another by setting the sum of the height of the protrusions20A and 20B to a value equal to the gap of the substrates, that is, thethickness of the liquid crystal layer. According to this arrangement,the spacer need not be used.

FIGS. 90A and 90B are diagrams showing the structure of a panel of the16th embodiment. FIG. 90A is a side view, and FIG. 90B is an obliqueview of a portion of the panel corresponding to one square of a lattice.FIG. 91 is a diagram showing a pattern of protrusions in the 16thembodiment which is seen in a direction vertical to the panel. Asillustrated, in the 16th embodiment, the protrusions 20A are createdlike a cubic lattice on the electrode 12 formed on one substrate, andthe pyramidal protrusions 20B are created at positions coincident withthe center positions of the opposite squares of the lattice on theelectrodes on the other substrate. In a region shown in FIG. 90B, theorientation is divided according to the principles described inconjunction with FIG. 12B and divided vertically and laterallyuniformly. In reality, a prototype was produced by setting the distancebetween the electrodes to 3.5 micrometers, the sideways spacing betweenprotrusions 20A and 20B to 10 micrometers, and the height of protrusionsto 5 micrometers. As a result, the viewing angle characteristic of thepanel was of the same level as the one of the panel of the secondembodiment shown in FIG. 22.

FIGS. 254A and 254B show a modification of the sixteenth embodiment.FIG. 254A shows a protrusion pattern and FIG. 254B is a sectional view.In this modification, the arrangement of the matrix-like protrusions andthe pyramidal protrusions of the sixteenth embodiment is reversed. Inother words, the protrusion 20A disposed on the electrode 12 of the CFsubstrate 16 is pyramidal whereas the protrusion 20B on the side of theTFT substrate 17 has a two-dimensional matrix form. The protrusion 20Ais disposed at the center of each pixel 9 and the protrusion 20B isdisposed in the same pitch as that of the pixels and is disposed on thebus line between the pixels 9. Therefore, the liquid crystal is orientedin four directions inside each pixel. The domain is divided by theprotrusion 20A at the center of the pixel as shown in FIG. 254B. Theprotrusion 20B disposed outside the pixel electrode 13 divides theorientation at the boundary of the pixels as shown in the drawing.Further, the edge of the pixel electrode functions at this portion asthe domain regulating means. The orientation regulating force by theprotrusion 20B and the orientation regulating force of the edge of thepixel electrode coincide with each other. Consequently, the division ofthe orientation can be carried out stably. In this modification, thedistances between the protrusion 20A and the protrusion 20B versus theedge of the pixel electrode 12 are great. Therefore, it is only theprotrusion 20A that exists inside the pixel, and the occupying area ofthe protrusion inside the pixel is small and display luminance can beimproved, though the response speed drops to a certain extent. Further,the production cost can be reduced by forming the protrusion 20B by theformation process of the bus line because the number of the productionsteps does not increase.

In the aforesaid first to 16th embodiments, protrusions produced using aresist that is an insulating material are used as a domain regulatingmeans for dividing the orientation of a liquid crystal. In theembodiments, the shape of the inclined surfaces of the protrusions areutilized. The insulating protrusions are very important in terms of theeffect of interruption of electric fields. A liquid crystal is drivenusing, generally, an alternating wave. With an increase in responsespeed deriving from innovation of a liquid crystal material, influenceexerted during one frame (during which a direct (dc) voltage isapplied), that is, influence predetermined by a DC wave must be takeninto full consideration. A driving wave for a liquid crystal mustexhibit both the characteristics of the AC and DC voltages and satisfythe requirements for the AC and DC voltages. The properties of theresist used to allow the driving wave for a liquid crystal to exert apredetermined effect of minimizing electric fields must be set inrelation to the characteristics of the AC and DC voltages or the AC andDC characteristics. Specifically, the resist must be set to haveproperties effective in minimizing electric fields in relation to the ACand DC characteristics.

From the viewpoint of the DC characteristic, the specific resistance ρmust be high enough to affect the resistance of a liquid-crystal layer.Specifically, the specific resistance must be 10¹² ohms/cm or more sothat it will be equal to or larger than the specific resistance of aliquid crystal (for example, the specific resistance of a TFT-driveliquid crystal is about 10¹² ohms/cm or more). Preferably, the specificresistance should be 10¹³ ohms/cm or more.

From the viewpoint of the AC characteristic, the capacitance (valuedetermined by a dielectric constant, film thickness, and sectional area)of a resist must be about ten or less times larger than the capacitanceof a liquid-crystal layer under the resist (with an impedance of aboutone-tenth or more of the impedance of the liquid-crystal layer), so thatthe resist can exert the operation of minimizing electric fields in theliquid-crystal layer under the resist. For example, the dielectricconstant ∈ of the resist is approximately 3 or about one-third of thedielectric constant ∈ of the liquid crystal layer (approximately 10).The film thickness is approximately 0.1 micrometers or about 1/35 of thethickness of the liquid-crystal layer (for example, approximately 3.5micrometers). In this case, the capacitance of the insulating film isapproximately ten times larger than the capacitance of theliquid-crystal layer under the insulating film. In other words, theimpedance of the resist (insulating film) is approximately one-tenth ofthe impedance of the liquid-crystal layer under the resist. Thus, theresist can affect the distribution of electric fields in theliquid-crystal layer.

In addition to an effect exerted by the shape of the inclined surfacescreated by the resist, the influence of the distribution of electricfields can be utilized. This results in more stable and firm alignment.When a voltage is applied, liquid crystalline molecules are tilted. Atthis time, the strength of electric fields in a domain in which theorientation of a liquid crystal is divided (on a resist) is sufficientlylow. In the domain, liquid crystalline molecules aligned nearlyvertically exist stably and work as a barrier (partition) againstdomains generated on both sides of the domain. When a higher voltage isapplied, the liquid crystalline molecules in the orientation-divideddomain (on the resist) starts tilting. However, the liquid crystallinemolecules in the domains generated on both sides of the domain on theresist tilt in a direction nearly horizontal to the resist (this resultsin a very firm orientation). For establishing this state, the insulatinglayer (resist) of the orientation-divided domain must have a capacitancethat is approximately ten or less times larger than the one of theliquid-crystal layer under the resist. A material exhibiting a smalldielectric constant ∈ should be adopted to realize the insulating layer,and the thickness of the layer must be large. This suggests aninsulating layer having a dielectric constant ∈ of approximately 3 and athickness of 0.1 micrometers or more. The employment of an insulatinglayer having a smaller dielectric constant ∈ and a larger thicknesswould exert a more preferable operation and effect. In the first to 16thembodiments, a novolak resist having a dielectric constant ∈ ofapproximately 3 is used to form protrusions of 1.5 micrometers thick.Observation of orientation division has revealed that very stablealignment can be attained. The novolak resist is widely adopted in theprocess of manufacturing a TFT or CF. The adoption of the novolak resistwould bring about a great merit (of obviating the necessity ofadditional facilities).

Moreover, it is ascertained that the novolak resist is highly reliableas compared with other resists or a flattening material and has noproblem.

Moreover, when the insulating film is placed on both substrates, a morepreferable operation and effect can be exerted.

Aside from the novolak resist, an acrylic resist (∈=3.2) was checked tosee if it would prove effective as an insulating film. The same resultsas those obtained by checking the novolak resist were obtained. Fordemonstrating that the influence of electric fields is very important,an ITO film was deposited on a resist and the aligned state of liquidcrystalline molecules was observed. The results were not so good asthose obtained when the insulating film was used.

In the first to 16th embodiments, an electrode is slitted or protrusionsof insulators are formed on an electrode in order to divide theorientation of a liquid crystal. Other forms can be adopted. Some of theforms will be presented below.

FIGS. 92A and 92B are diagrams showing the structure of a panel of the17th embodiment. FIG. 92A is an oblique view and FIG. 92B is a sideview. As illustrated, in the 17th embodiment, protrusions 50 extendingparallel to one another unidirectionally are formed on glass substrates16 and 17, and electrodes 12 and 13 are formed on the substrates. Theprotrusions 50 are arranged to be mutually offset by a half pitch. Theelectrodes 12 and 13 are therefore shaped to partly jut out. Thesurfaces of the electrodes are processed for vertical alignment. Usingthe thus shaped electrodes, when a voltage is applied to the electrodes,electric fields are induced in a vertical direction. The orientation ofa liquid crystal is divided into two directions with each protrusion asa border. The viewing angle characteristic of the panel is thereforeimproved as compared with a conventionally exhibited one. However, thedistribution of electric fields becomes different from the one attainedwhen the protrusions are made of an insulating material. Only the effectof the shape of the inclined surfaces of the protrusions is utilized inorder to divide the orientation. The stability of alignment is slightlyinferior to that attained when the protrusions are made of an insulatingmaterial. However, as described above, the protrusions provided on theelectrodes need to be made of insulating material with low dielectricconstant. Therefore, the materials used to form the protrusions arelimited. Further, various conditions must be satisfied to form theprotrusions by using those materials. This causes a problem in theproduction process. Contrarily, the panel structure of the 17thembodiment does not have such limitation.

FIG. 93 is a diagram showing the structure of a panel of the 18thembodiment. In this embodiment, insulating layers 61 formed on the ITOelectrodes 12 and 13 are provided with depressions 23. As the shape ofthe depressions, the shapes of protrusions or slits of electrodespresented in the second to ninth embodiments can be adopted. In thiscase, an effect exerted by oblique electric fields works like the effectexerted by the protrusions to stabilize alignment.

FIG. 94 shows a panel structure of the nineteenth embodiment. In thisembodiment, electrodes 12 and 13 are formed on glass substrates 16 and17, respectively, layers 62 each made of an electrically conductivematerial and having a depression (groove) 23A, 23B having a width of 10μm and a depth of 1.5 μm are formed on these electrodes 12 and 13, andvertical alignment films 22 are formed on these layers 62. Incidentally,the thickness of a liquid crystal layer is 3.5 μm, and a color filterlayer 39, a bus line, a TFT, etc, are omitted from the drawing. It canbe observed that the orientation of the liquid crystal is divided at therecess portions. In other words, it has been confirmed that thedepression, too, functions as the domain regulating means.

In the panel structure of the nineteenth embodiment, the depressions 23Aand 23B are disposed at the same predetermined pitch of 40 μm in thesame way as in the case of the protrusions, and the upper and lowerdepressions 23A and 23B are so disposed as to deviate by a half pitch.Therefore, the regions in which the liquid crystal assumes the sameorientation are defined between the adjacent upper and lowerdepressions.

FIG. 95 shows the panel structure of the 20th embodiment. In this 20thembodiment, layers 62 having grooves 23A and 23B having a width of 10 μmand a depth of 1.5 μm are formed on the glass substrates 16 and 17 byusing a color filter (CF) resin, respectively, electrodes 12 and 13 areformed on these layers 62, and vertical alignment films are furtherformed on the electrodes 12 and 13, respectively. In other words, a partof each electrode 12, 13 is recessed. The protrusions 23A and 23B aredisposed at the same predetermined pitch of 40 μm whereas the upper andlower depressions 23A and 23B are so disposed as to deviate from oneanother by a half pitch. In this case, too, the same result as that ofthe nineteenth embodiment can be obtained. Incidentally, since thestructure having the depression is disposed below the electrode in this20th embodiment, limitation to the material is small, and the materialused for other portions such as the CF resin can be used.

In the case of the protrusion and the slit, the orientation is dividedin such a fashion that the liquid crystalline molecules expand in theopposite direction at these portions but in the case of the recess, theorientation is divided in such a fashion that the liquid crystallinemolecules face one another at the depression portion. In other words,the function of dividing the orientation by the recess has the oppositerelation to that of the protrusion and the slit. Therefore, when thedepression is used as the domain regulating means in combination withthe protrusion or the slit, the preferred arrangement becomes oppositeto the arrangements of the foregoing embodiments. The explanation willbe predetermined next on the arrangement when the recess is used as thedomain regulating means.

FIG. 96 shows an example of the preferred arrangements when thedepression and the slit are used in combination. As shown in thedrawing, the slits 21A and 21B are disposed at positions opposing thedepressions 25-23A and 23B of the 20th embodiment shown in FIG. 95.Since the direction of the orientation division of the liquid crystal bythe depressions and the slits opposing one another is the same, theorientation is further stabilized. For example, when the depression isformed under the condition of the 20th embodiment, the slit has a widthof 15 μm and the gap between the center of the depression and that ofthe slit is 20 μm, the switching time is 25 ms under the drivingcondition of 0 to 5 V and 40 ms under the driving condition of 0 to 3 V.In contrast, when only the slit is used, the switching time is 50 ms and80 ms, respectively.

FIG. 97 shows the structure wherein the depression 20A and the slit 21Aon one of the substrates (substrate 16 in this case) in the panelstructure shown in FIG. 98, and the region having the same orientationdirection is formed between the adjacent depression 20B and the slit21B.

Incidentally, the same characteristics can be obtained by disposing theprotrusion at the same position in place of the slit in the panelstructures shown in FIGS. 96 and 97, and the response speed can befurther improved.

FIG. 98 shows another panel structure wherein the depression 23B isformed in the electrode 13 of the substrate 17 and the protrusions 20Aand the slits 21A are alternately formed at positions of the opposedsubstrate 16 at positions facing the depression 23B, respectively. Inthis case, the direction of the orientation becomes different betweenthe set of the adjacent depression 23B and protrusion 20A and the set ofthe adjacent depression 23B and slit 21A and consequently, the boundaryof the orientation regions is formed in the proximity of the center ofthe depression.

FIGS. 99A and 99B are diagrams showing the structure of a panel of the21th embodiment. As illustrated, the panel of the 21th embodiment is asimple matrix LCD. The surface of each electrode is dented. Theorientation of a liquid crystal is divided with each depression as aborder. However, like the tenth embodiment, an effect of obliqueelectric fields is not exerted. The stability of alignment is littlepoor.

As described above, the alignment dividing operation of depressions(grooves) is reversed to those of protrusions and slits. By using thisrelation, a ratio of domain areas can be constant regardless of assemblyerrors. Now, the influence of assembly errors in the panel of the firstembodiment will be described.

FIGS. 100A and 100B are sectional views of a panel in the firstembodiment. As described already, a region where the orientation isregulated is defined by the protrusion 20A formed on the commonelectrode 12 and the protrusion 20B formed on the cell electrode 13. InFIG. 100A, the region defined by the right inclined side surface of theprotrusion 20B and the left inclined side surface of the protrusion 20Ais designated as a region A, and the region defined by the left inclinedside surface of the protrusion 20B and the right inclined side surfaceof the protrusion 20A is designated as a region B.

Assume that the CF substrate 16 is displaced leftward of the TFTsubstrate 17 due to an assembly error, as shown in (2) FIG. 100B. Theregion A is reduced, while the region B increases. Therefore, the ratiobetween region A and region B is not already 1 to 1. The resultingproportion of liquid crystalline molecules divided in orientation is notequal, thereby deteriorating the viewing angle characteristic.

FIGS. 101A and 101B are sectional views of a panel according to a 22thembodiment. In the 22th embodiment, as shown in FIG. 101A, a depression22B and a protrusion 20B are formed in the TFT substrate 17, followed byforming a depression 20A and a protrusion 22A on the CF substrate 16.This process is repeated. As shown in FIG. 101B, assuming that the CFsubstrate is displaced with respect to the TFT substrate 17 at the timeof assembly, the region A′ defined by the protrusions 20B and 20A isreduced. Since the region A″ defined by the depressions 22B and 22A isincreased by the same amount as the region A′ is reduced, however, theregion A remains unchanged. The region B, which is defined by theprotrusion 20B, the depression 22B, the protrusion 20A and thedepression 22A, remains unchanged since the interval between themremains unchanged. Consequently, the ratio between the regions A and Bremains the same, and the superior viewing angle characteristic ismaintained.

FIG. 102 is a sectional view of a panel according to a 23th embodiment.In the 23th embodiment, as shown, the CF substrate 16 is formed with theprotrusions 22A and the depressions 20A alternately with each other.This process is repeated. The region A is defined by the left inclinedside surface of the protrusion 20A and the right inclined side surfaceof the depression 22A, while the region B is defined by the rightinclined side surface of the protrusion 20A and the left inclined sidesurface of the depression 22A. In view of the fact that the orientationregion is defined only by the protrusions and depressions formed on oneof the substrates, the assembly accuracy is not affected.

The foregoing embodiments are directed to obtain a great viewing anglein all directions. Depending on the application of the liquid crystalpanel, however, there are the cases where the viewing angle need not begreat, and a great viewing angle needs be obtained in only a specificdirection. The LCD suitable for such an application can be accomplishedby using the orientation dividing technology by the domain regulatingmeans described above. Next, several embodiments to which the technologyof the present invention is applied for the LCDs for such specificapplications will be explained.

FIGS. 103A and 103B show the panel structure of the 24th embodiment.FIG. 103A is a top view and FIG. 103B is a sectional view taken along aline Y-Y′ of FIG. 103B. Linear protrusions 20A and 20B are disposed inthe same pitch on substrates 16 and 17, respectively, as shown in thedrawing, and these protrusions 20A and 20B are so situated as to deviatea little from the respective opposing positions. In other words, theregion B is extremely narrowed in the structure shown in FIG. 102 sothat the regions are occupied almost fully by the region A.

The panel of the twenty-fourth embodiment is used for a protrusion typeLCD, for example. The viewing angle performance of the protrusion typeLCD may be narrow, but a high response speed, a high contrast and highluminance are required for the protrusion type LCD. Since theorientation direction of the panel of the 24th embodiment issubstantially in one direction (mono-domain), the viewing angleperformance is the same as those of the conventional VA system andcannot be said as excellent. Nonetheless, since the protrusions 20A and20B are disposed, the response speed is improved markedly in comparisonwith the conventional system, in the same way as the LCDs of theforegoing embodiments. As to contrast, the contrast of this panel issubstantially equal to other VA system and is therefore superior to thatof the conventional TN mode and IPS mode. As has been explained alreadywith reference to FIG. 27, the orientation gets distorted and leakinglight transmits through the portions of the protrusions 20A and 20B. Toimprove contrast, therefore, the portions of these protrusions 20A and20B are preferably shaded. As to luminance, on the other hand, theaperture ratio of the pixel electrode 13 is preferably increased.Therefore, the protrusions 20A and 20B are disposed at the edge of thepixel electrode 13 as shown in FIGS. 103A and 103B. This arrangement canincrease luminance without lowering the aperture ratio.

From the aspect of the response speed, the gap between the protrusions20A and 20B is preferably decreased but to attain this object, theprotrusions 20A and 20B must be disposed around the pixel electrode 13.When the protrusions 20A and 20B are disposed around the pixel electrode13, these portions must be shaded, so that the aperture ratio drops asmuch. As described above, the response speed, the contrast and luminancehave the trade-off relationship, and they must be set appropriatelydepending on the object of use, and so forth.

FIG. 104 shows a structure for achieving an LCD panel having excellentviewing angle performance in three directions by utilizing thetechnology of forming the mono-domain according to the 24th embodiment.In this structure, the protrusions 20A and 20B are disposed in such afashion as to define two regions of the transverse direction in the sameproportion and one region of the longitudinal orientation inside onepixel. The two regions of the transverse orientation in the sameproportion are formed by so disposing the protrusions 20A and 20B as todeviate from one another by a half pitch as shown in FIGS. 100A and100B, while one region of the longitudinal orientation is formed bydisposing the protrusions 20A and 20B adjacent to one another as shownin FIGS. 103A and 103B. This structure can accomplish a panel which hasexcellent viewing angle performance on the right and left sides and onthe lower side but has lower viewing angle performance on the upperside.

The LCD such as of the 24th embodiment is used for a display which isinstalled at a high position so that a large number of people look it upfrom below, such as a display device disposed above a door of a train.

As shown in FIG. 85C, the LCD of the VA system which does not executethe orientation division and the LCD of the VA system which execute theorientation division by the protrusions or the like, the response speedfrom black to white and vice versa is superior to that of the TN mode,but the response speed between the intermediate gray-scale is notpractically sufficient. The twenty-fifth embodiment solves this problem.

FIGS. 105A and 105B show the panel structure in the 25th embodiment.FIG. 105A shows the shape of the protrusion when viewed from the panelsurface and FIG. 105B is a sectional view. As shown in these drawings,the position of the protrusion 20B is charged inside one pixel so as todefine a portion having a different gap with the protrusion 20A. Inconsequence, the proportion of the domain oriented in two directions canbe made equal and the viewing angle performance is symmetric. When thestructure shown in the drawings is employed, the response speed betweenthe intermediate gray-scale can be apparently improved. This principlewill be explained with reference to FIGS. 106 to 109B.

FIG. 106 shows the structure of the panel manufactured for measuring thechanges of the response speed and the transmittance depending on the gapof the protrusions. The protrusions 20A and 20B have a height of 1.5 μmand a width of 10 μm, and the thickness of the liquid crystal layer is3.5 μm. The response speed and the transmittance of the region of thegap d1 and the region of the gap d2 are measured by setting one of thegaps d1 of the protrusions to 10 μm, changing the other gap d2 andchanging also the voltage to be applied across the electrodes between 0Vand 3 V corresponding to the intermediate gray-scale.

FIG. 107 is a graph showing the result of the response speed measured inthe way described above. This graph corresponds to the one obtained byextracting the object portion shown in FIGS. 20A and 20B. As can be seenclearly from the graph, the response time drops as the gap d2 becomessmaller.

FIG. 108A shows the change of the transmittance when the applied voltageis changed, by using the gap d2 as a parameter. FIG. 108B shows thechange of the transmittance when the voltage is changed from 0V to 3V byusing the gap d2 as a parameter. It can be seen from FIGS. 108A and 108Bthat the response speed of the intermediate gradation can be drasticallyimproved by decreasing the gap d2 of the protrusions. However, themaximum transmittance drops when the gap d2 of the protrusions isdecreased.

FIG. 109A is a graph showing the normalized time change of thetransmittance at each gap d2, and FIG. 109B explains the orientationchange of the liquid crystal. Assuming that the time before thetransmittance reaches 90% of the maximum transmittance is an ON responsetime, the ON response time when d2 is 10 μm is Ton 1, the ON responsetime when d2 is 20 μm is Ton 2 and the ON response time when d2 is 30 μmis Ton 3, they have a relationship of Ton 1<Ton 2<Ton 3.

The reason why such a difference occurs is because only the liquidcrystals in the proximity of the protrusion are oriented perpendicularlyto the slope of the protrusion and the liquid crystals away from theprotrusion are oriented perpendicularly to the electrode when thevoltage is not applied, as shown in FIG. 109B. When the voltage isapplied, the liquid crystal is inclined, and the liquid crystal can takethe tilt angle of up to 360 degrees with respect to the axisperpendicular to the electrode. The liquid crystal in the proximity ofthe protrusion is oriented when the voltage is not applied, and theliquid crystal between the protrusions is oriented in such a fashion asto extend along the former liquid crystal as the trigger. In this way isformed the domain in which the liquid crystals are oriented in the samedirection. Consequently, the closer to the liquid crystal to theprotrusion, the more quickly it is oriented.

As described above, the response time between black and white issufficiently short in the existing VA system LCDs and it is the responsetime between the intermediate gray-scale that becomes the problem. Inthe case of the structure shown in FIGS. 105A and 105B, thetransmittance in the regions having a narrow gap d2″ changes within ashort time whereas the transmittance in the regions having a broad gapd2′ changes gradually. The regions of the gap d2″ are narrower than theregions of the gap d2′ and have a smaller contribution to thetransmittance, but because the human eyes have logarithmiccharacteristics, the human eyes catch the change as a relatively largechange when the transmittance in the regions of the small gap d2″changes a little. Therefore, if the transmittance of the regions havinga small gap d2″ changes within a short time, this change is caught asthe drastic change as a whole.

As described above, the panel according to the 25th embodiment canapparently improve the response speed between the intermediategray-scale without lowering the transmittance.

FIG. 110 shows the panel structure of the 26th embodiment. As shown inthe drawing, the protrusions 20A and 20B are disposed in an equal pitchon the substrates 16 and 17 and the electrodes 12 and 13 are formed onthe protrusions, respectively, in this 26th embodiment. However, theelectrodes are not formed on one of the slopes of the protrusions 20Aand 20B, and a vertical alignment film is further formed. Theprotrusions 20A and 20B are arranged in such a fashion that the slopeson which the electrode is formed and the slopes on which the electrodeis not formed are adjacent to one another. In the region between theslopes on which the electrodes are not formed, the liquid crystals areoriented perpendicularly to the slopes, and the orientation direction isdecided consequently. The electric field in the liquid crystal layer isrepresented by broken lines in the drawing. Since the liquid crystalsare oriented along this electric field, the orientation direction due tothe electric field in the proximity of the slopes, on which theelectrodes are not formed, coincides with the orientation direction dueto the slopes.

In the region between the slopes on which the electrode is formed, onthe other hand, the liquid crystal in the proximity of the slopes isoriented perpendicularly to the slopes, but the orientation direction ofthe electric field in this region is different from the orientationdirection due to the slopes. Therefore, the liquid crystal in thisregion is oriented along the electric field with the exception of theportions near the slopes when the voltage is applied. Consequently, theorientation directions in the two regions become equal to each other,and the mono-domain orientation can be obtained.

FIG. 111 shows the viewing angle performance with respect to contrastwhen a phase difference film having negative dielectric constantanisotropy and having the same retardation as that of the liquid crystalpanel is superposed with the panel of the 26th embodiment. A highcontrast can be obtained over a broad range of viewing angles.Incidentally, when this panel is assembled into the protrusion typeprojector, the contrast ratio is at least 300. Incidentally, thecontrast ratio obtained when the ordinary TN mode LCD is assembled intothe protrusion type projector is about 100, and it can be appreciatedthat the contrast ratio can be drastically improved.

In the case where a liquid crystal display device having a configurationwith a protrusion pattern is driven as in the first embodiment, thedisplay quality is seen to deteriorate in the neighborhood of the busline (gate bus line or data bus line) in the pixel. This is due to theundesirable minute region (domain) formed in the neighborhood of the busline and the resulting disturbance of liquid crystal orientation andreduced response rate. The problem thus is posed of a reduced viewingangle characteristic and a reduced color characteristic in half tone.This problem is solved in a 27th Embodiment.

FIG. 112 is a diagram showing an example pattern for repeating thelinear protrusions according to the embodiments as set above. Theprotrusion pattern described above has a plurality of protrusions of apredetermined width and a predetermined height repeated at predeterminedpitches. In FIG. 112, therefore, the width 1 and the interval m assumeof the protrusion assume the predetermined values of 11 and m1,respectively. In the shown example, the width of the protrusion formedon one substrate is different from that of the protrusion formed on theother substrate. The protrusions formed on a substrate, however, have apredetermined width l. This is also the case with the protrusion heighth.

FIG. 113 is a diagram showing the wavelength dispersion characteristicof the optical anisotropy of the liquid crystal used. As shown, it isseen that the shorter the wavelength, the larger the retardation Δn.Thus, the retardation Δn increases in the order of blue (B) pixel, green(G) pixel and red (R) pixel, and different colors have differentretardation Δn while passing through the liquid crystal layer. Thisdifference is desirably as small as possible.

FIG. 114 is a diagram showing a protrusion pattern according to a 27thembodiment of the invention. In the 27th embodiment, the blue (B) pixel13B, the green (G) pixel 13G and the red (R) pixel 13R each have thesame protrusion width l but different protrusion intervals m.Specifically, the B pixel 13B has m1, the G pixel 13G m2 and the R pixel13R m3 in such a relation that m1>m2>m3.

The smaller the protrusion interval m, the larger the effect that theelectric field vector has on the liquid crystalline molecules, thusmaking it more possible to alleviate the problem of the electric fieldvector at the time of drive. FIG. 115 is a diagram showing the relationbetween the applied voltage and the transmittance as measured whilechanging the protrusion interval. It is seen that the larger theinterval m, the larger the numerical aperture, and hence thetransmittance is improved. The wavelength dispersion characteristic ofthe optical anisotropy of the liquid crystal is as shown in FIG. 113. Bychanging the protrusion interval m for each color pixel as shown in FIG.114, the difference of the retardation for a particular color can bereduced Δn while passing through the liquid crystal layer for animproved color characteristic.

FIG. 116 is a diagram showing a protrusion pattern according to a 28thembodiment of the invention. In the seventh embodiment, the blue (B)pixel 13B, the green (G) pixel 13G and the red (R) pixel 13R have thesame protrusion interval m but different protrusion widths 1. The effectis the same as that of the 27th embodiment.

FIG. 117 is a diagram showing a protrusion pattern according to an 29thembodiment of the invention. In the 29th embodiment, the protrusioninterval m in each pixel is set to a small value m1 in the upper andlower regions near to the gate bus line and a large value m2 at thecentral region. In the neighborhood of a bus line such as the gate busline or the data bus line, a domain may occur at the time of driving andthe liquid crystalline molecules fall into a state not suitable fordisplay due to the electrical field vector, thereby deteriorating thedisplay quality. According to the eighth embodiment, the protrusioninterval is narrowed in the region near to the gate bus line thereby tomake it difficult for the gate bus line to be affected by the electricalvector. As a result, the generation of an undesirable domain issuppressed for an improved display quality. However, a narrowerprotrusion interval reduces the numerical aperture accordingly anddarkens the display. From the viewpoint of numerical aperture,therefore, a larger protrusion interval is recommended. The protrusionpattern according to the eighth embodiment can minimize the reduction innumerical aperture and reduce the effect of the electrical field vectorgenerated by the gate bus line.

FIG. 118 is a diagram showing the pixel structure in the case where theprotrusion pattern according to the 29th embodiment shown in FIG. 117 isactually realized.

FIG. 119 is a diagram showing a protrusion arrangement according to a30th embodiment. As shown in FIG. 119, in the 30th embodiment, theprotrusion height is changed gradually.

FIG. 120 is a diagram showing the change that the relation between theapplied voltage and the transmittance undergoes when the protrusionheight is changed, FIG. 121 the change that the relation between theapplied voltage and the contrast undergoes when the protrusion height ischanged, FIG. 122 the change of the transmittance in white level withrespect to the protrusion height, and FIG. 123 the change of thetransmittance in black level with respect to the protrusion height.These diagrams show the result of measuring the transmittance and thecontrast in test equipment with the width and interval of the resist forforming the protrusion set to 7.5 μm and 15 μm, respectively, the cellthickness to about 3.5 μm, and the resist height to 1.537 nm, 1.600 nm,2.3099 nm and 2.486 nm.

This measurement shows that the transmittance of white level (with 5 Vapplied) increases with the resist height. This is considered due to thefact that the protrusion playing an auxiliary role in tilting the liquidcrystal is so large that the liquid crystal is positively fallen. Thetransmittance (leakage light) in black level (without any appliedvoltage) also increases with the protrusion height. This is notdesirable as it works to deteriorate the black level. The contrast(ratio between white luminance and black luminance) decreases with theprotrusion height. It is therefore desirable to use a masking materialfor the protrusion and not to increase the protrusion heightexcessively.

Any way, the orientation of the crystal liquid can be changed bychanging the protrusion height, and therefore a superior display is madepossible by changing the protrusion height for each color pixel and thusadjusting the color characteristic, or by setting the protrusion heightappropriately in accordance with the distance from the bus line. For theR pixel, for example, the protrusion height is increased, and decreasedfor the G pixel and the B pixel in that order, or in each pixel, theprotrusion height is increased in the neighborhood of the bus line andlowered at the central portion.

The inventor has confirmed that the screen display can be accomplishedwithout any problem even when the protrusion height is increased to thesame level as the cell thickness. As a result, the protrusion height isset to the same level as the cell thickness as shown in FIG. 124A, orprotrusions are formed at the opposed positions on the two substrates asshown in FIG. 124B so that the sum of the heights of the two protrusionsis the same as the cell thickness. In this way, the protrusion can playthe role of a panel spacer.

FIGS. 125A and 125B are diagrams showing a protrusion pattern accordingto a 31th embodiment. In this embodiment, as shown in FIG. 125A, theinclination of the side surfaces of the protrusion is defined by theangle θ that the side surface forms with the substrate (electrode). Thisangle is called the taper angle. According to the tenth embodiment,assume that the taper angle θ of the protrusion 20 can take severalvalues as shown in FIG. 125B. Generally, the larger the taper angle θ,the more satisfactory the orientation into which the liquid crystallinemolecules fall. By changing the taper angle θ, therefore, theorientation of the liquid crystal can be changed. Thus, a superiordisplay can be made possible by changing the taper angle for each colorpixel to adjust the color characteristic or by setting a proper taperangle θ in accordance with the distance from the bus line. For example,the taper angle θ is set large for the R pixel, and decreased for the Gpixel and the B pixel in that order. Also, the taper angle θ isincreased in the neighborhood of the bus line and decreased at thecentral portion in a pixel.

As described above with reference to the sixth to tenth embodiments, theorientation regulation force of the protrusion is changed by changingthe protrusion interval, protrusion width, protrusion height or taperangle. It is therefore possible that these conditions are differentiatedwithin a pixel or with different color pixels to partially differentiatethe orientation regulation force of protrusions and thus to assure theviewing angle characteristic or response rate of the liquid crystal asnear to the ideal ones as possible.

Retardation of the liquid crystal depends on the wavelength as shown inFIG. 113. Therefore, an embodiment of the liquid crystal panel whichimproves luminance of white display on the basis of this feature andaccomplishes a high response speed for all the color pixels will beexplained.

First, wavelength dependence of the VA system will be explained briefly.FIG. 126 shows the change of a twist angle of a liquid crystal layer dueto the application of a voltage when a vertical orientation (VA) systemliquid crystal display panel using a liquid crystal having negativedielectric anisotropy (n type liquid crystal) is provided with the twistangle. When no voltage is applied, the liquid crystal is oriented in adirection of 90 degrees on the surface of one of the substrates and in adirection of 0 degree on the surface of the other substrate, so that thetwist of 90 degrees is attained. When the voltage is applied under thisstate, only the liquid crystalline molecules in the proximity of thesurface of the substrate undergo twisting in such a manner as to followthe anchoring energy of the substrate surface, but twisting hardlyoccurs in other layers. Therefore, the mode does not substantiallychange to the rotatory polarization mode (TN mode) but to thebirefringence mode. FIG. 127 shows the change of relative luminance(transmittance) to the change of the retardation Δnd (d; μm) in both theTN mode and the birefrigence mode. As shown in the graph, thebirefringence mode exhibits sharper transmittance characteristics to Δndof the liquid crystal than the TN mode. As described above, the verticalorientation liquid crystal using the n type liquid crystal executesblack display when no voltage is applied and white display when thevoltage is applied, by using the polarizer plate as the cross-Nicol.

FIG. 128 shows the change of the transmittance to the change of Δnd ateach wavelength (R: 670 nm, G: 550 nm, B: 450 nm). It can be appreciatedfrom this graph that when the thickness of the liquid crystal layer isset to Δnd at which luminance in white display attains the maximum, thatis, to Δnd at which the transmittance attains the maximum at thewavelength of 550 nm, the transmittance at 450 nm becomes excessivelylow. Therefore, the thickness of the liquid crystal layer is set to avalue smaller than the thickness determined from maximum luminance so asto restrict coloring in white display. Therefore, luminance in whitedisplay is lower than that of the TN mode, and in order to obtain whiteluminance equivalent to that of the liquid crystal display panel of theTN mode, back-light luminance must be increased. To increase thisback-light luminance, however, power consumption of illumination must beincreased, and the range of application of the panel is limited. Whenthe thickness of the liquid crystal layer is increased by laying stresson white luminance, the transmittance becomes excessively low at 450 nmin comparison with the TN mode, and the panel is colored yellow in whitedisplay.

To enlarge the viewing angle range, on the other hand, it has beencustomary to add a phase difference film, but when the thickness of theliquid crystal layer becomes great, the color change in the direction ofthe critical angle (transverse direction) becomes so great that even ifthe retardation value of the phase difference film is the same, thecolor difference becomes greater.

In the 32th embodiment, the thickness of the liquid crystal layer ofeach color pixel is individually set so that the transmittance becomesmaximal when the driving voltage is applied. However, when the thicknessof the liquid crystal layer is different, a difference occurs in theresponse speed and the color tone cannot be displayed correctly when theoperation display is carried out. Therefore, when the thickness of theliquid crystal layer is set to a different value for each color pixel,means for making uniform the response speed of the liquid crystalbecomes necessary.

FIG. 129 shows the change of the liquid crystal response speed to thegap of the protrusions or the slits when Δnd of the liquid crystal layeris set so that the maximum transmittance can be obtained at the threekinds of wavelengths described above. The liquid crystal response speedbecomes lower as the thickness of the liquid crystal layer becomesgreater. In the VA system LCD panel which controls the orientation byusing the protrusion, the liquid crystal response speed changes with thedielectric constant of the protrusion, the shape of the protrusion, theprotrusion gap, and so forth. However, when the dielectric constant, theshape of the protrusion and its height are constant, the response speedbecomes higher when the gap of the protrusions is narrower. It can beappreciated that to obtain the liquid crystal response speed of 25 ms,for example, in FIG. 129, the gap of the protrusions or the slits mustbe set to 20 μm for the R pixel, 25 μm for the G pixel and 30 μm for theB pixel.

FIG. 130 shows the change of the aperture ratio with respect to theprotrusion or slit gap. When the gap of the protrusions or the slits isset to 20 μm for the R pixel, 25 μm for the G pixel and 30 μm for the Bpixel from FIG. 129 the transmittance is 80%, 83.3% and 85.7%,respectively, and the differences occur in the transmittance.

In view of this point the 32nd embodiment individually sets thethickness of the liquid crystal layer of each color pixel so that thetransmittance attains the maximum when the driving voltage is applied,the response speed in each color pixel is rendered coincident byregulating the gap of the protrusions, and the area of each color pixelis changed so that the transmittance becomes coincident.

FIG. 131 shows the panel structure of the 32nd embodiment. As shown inthis drawing, a structure 71 not having the R pixel portion but havingthe G pixel portion having a thickness of 0.55 μm and the B pixelportion having a thickness of 1.05 μm is provided to both substrates 16and 17. The optimum condition is calculated for this thickness bysimulation for the VA system birefringence mode using the n type liquidcrystal. Further, the height of the protrusion 20A is set to 2.45 μm forthe R pixel, 1.9 μm for the G pixel and 1.4 μm for the B pixel. Further,the gap of the protrusions is set to 20 μm for the R pixel, 25 μm forthe G pixel and 30 μm for the B pixel. The area ratio of the B pixel:Gpixel:R pixel is set to 1:1.03:1.07. In other words, the pixel areas areso set as to satisfy the relation R pixel>G pixel>B pixel.

The structure 71 uses an acrylic resin, and after a resist is applied toa thickness of 1.4 μm for the B pixel, a protrusion having a width of 5μm is formed by photolithography. After a vertical alignment film isapplied, a 3.6 μm spacer is sprayed to form a seal, and after bondingand curing of the seal, the liquid crystal is charged. In this way, thethickness of the liquid crystal layer is 5.7 μm for the R pixel, 4.6 μmfor the G pixel and 3.6 μm for the B pixel.

FIG. 132 shows the panel structure of a modification of the 32thembodiment, wherein a protrusion is formed on the CF substrate 16 and aslit 21 is formed on the pixel electrode 13 of the TFT substrate 17. Inthis modification, an acrylic resin structure 71 not having the R pixelportion but having the G pixel portion having a thickness of 1.1 μm andthe B pixel portion having a thickness of 2.1 μm is provided to the CFsubstrate 16. After a resist is applied to a thickness of 1.4 μm for theB pixel, a protrusion having a width of 5 μm is formed byphotolithography. As a result, the height of the protrusion is 3.5 μmfor the R pixel, 2.5 μm for the G pixel and 1.4 μm for the B pixel. Thegap between the protrusion 20A and the slit is set to 20 μm for the Rpixel, 25 μm for the G pixel and 30 μm for the B pixel. The area ratioof the B pixel:G pixel:R pixel is set to 1:1.03:1.07.

A biaxial phase difference film (retardation value: 320 nm) in matchwith nd of the liquid crystal layer of the G pixel is added to thepanels of the 32th embodiment and to its modification produced in themanner described above, and the color difference is measured for each ofthe panel transmittance, the viewing angle and the critical angledirection (0 to 80 degrees). The results are shown in FIG. 249. By theway, the measurement results obtained by changing the thickness of theliquid crystal layer in the prior art example are also shown in FIG. 249as the reference values.

As can be appreciated from FIG. 249 the transmittance (luminance) infront can be increased by increasing the thickness of the liquid crystallayer to improve the transmittance as represented by the prior artexample 1, but because the length of the optical path gets elongated inthe direction of the critical angle, the transmittance of the squarewavelength fluctuates greatly and the color difference becomes great. Incontrast, in the panels of the 32th embodiment and its modification, thegap of the protrusions or the slits is narrowed for the R and G pixelsso as to make uniform the response speed of the liquid crystal, and thetransmittance becomes lower than that of the prior art example 2 as theaperture ratio is lower. Nonetheless, because the thickness of eachliquid crystal layer is set so that the transmittance attains themaximum when the driving current is applied (white display), the colordifference in the direction of the critical angle becomes small.

The panels according to the 32th embodiment and its modification canbrighten white-luminance to the level equal to the TN mode withoutcausing coloration of the panels in the broad range of the viewingangles. Because the liquid crystal response speed is made uniform so asto correspond to the thickness of each liquid crystal layer, display canbe obtained with high color reproducibility even when dynamic imagedisplay is made.

Next, processes for forming protrusions will be described.

When protrusions are formed on electrodes 12, 13 of a CF substrate 16and a TFT substrate 17, the electrodes of ITO film are formed, then, aresist is coated on the surfaces and is patterned with aphotolithography. This process is easily carried out by usingconventional techniques.

However, this process needs a step of creating the pattern ofprotrusions. If protrusions can be formed on the TFT substrate byutilizing the conventional process as it is, an increase in number ofsteps can be avoided. For forming insulating protrusions, it is thoughtthat an insulating layer used in the conventional process is furtherpatterned in order to leave the pattern of protrusions intact. Forcreating conducting protrusions, a conductive layer used in theconventional process is further patterned in order to leave the patternof protrusions intact

FIG. 133 is a diagram showing the structure of a TFT substrate in the33th embodiment. The thirteenth 33th provides a structure in which aninsulating layer used in the conventional process is utilized forcreating insulating protrusions. In this structure, the ITO electrodes13 are formed first. An insulating layer is formed on the ITO electrodesand portions of the insulating layer coincident with the ITO electrodes13 are removed. At this time, portions of the insulting layer coincidentwith protrusions 68 are left intact. The gate electrodes 31 are thenformed. An insulating layer is formed and portions of the insulatinglayer other than necessary portions are removed. At this time, if theprotrusions are required to have a certain thickness, portions of theinsulating layer coincident with the protrusions 68 are left intact.Thereafter, data bus lines and TFTs are formed in the same manner as aconventional process. In the drawing, reference numeral 41 denotes adrain (data bus line), 65 denotes a channel protective film, 66 denotesa wiring layer used to separate devices, and 67 denotes an operatinglayer for transistors. The ITO electrodes 13 and sources are linked byholes

FIGS. 134A and 134B are diagrams showing examples of a pattern ofprotrusions manufactured according to the process described inconjunction with the 33th embodiment. FIG. 134A shows linear andparallel protrusions used to divide an orientation-divided domain intotwo regions, and FIG. 134B shows zigzag protrusions used to divide anorientation-divided domain into four regions. In the drawings, referencenumerals 68 denotes a protrusion, and 69 denotes a pixel.

FIG. 135 is a diagram showing the structure of a panel of the 34thembodiment. The 34th embodiment provides a structure in which aconductive layer used in the conventional process is utilized forforming conducting protrusions. In this structure, first, a TFTlight-interceptive metallic layer 70 for intercepting light from TFTs isformed, an insulating layer is formed on the metallic layer 70, and ITOelectrodes are formed thereon. An insulating layer is formed furtherthereon, data bus lines and TFTs are then formed, and an insulatinglayer is formed further thereon. A layer of gate electrodes 31 is thenformed. The insulating layer is removed except portions thereofcoincident with the gate electrodes. At this time, portions of theinsulating layer coincident with the protrusions 20B are left intact

FIGS. 136A and 136B show examples of a pattern of protrusionsmanufactured as described in conjunction with the 34th embodiment. FIG.136A shows linear and parallel protrusions used to divide anorientation-divided domain into two regions, and FIG. 136B shows zigzagprotrusions used to divide an orientation-divided domain into fourregions. In the drawings, reference numeral 20B denotes a protrusion.Reference numeral 35 denotes a CS electrode. The CS electrodes 35 areextending along the edges of pixel electrodes so as to work as blackmatrices, but are separated from the protrusions 20B. This is becausethe CS electrodes 35 apply a certain voltage to the pixel electrodes(ITO electrodes) 13, and that if the voltage were applied to theprotrusions 20B, alignment of liquid crystalline molecules would beadversely affected

FIGS. 137A to 137D show a process for manufacturing the TFT substrate ofthe panel of the 35th embodiment. As shown in FIG. 137A, the gateelectrode 31 is patterned on the glass substrate 17. Next, the SiNxlayer 40, the amorphous silicon (α-Si) layer 72 and the SiNx layer 65are serially formed. Further, as shown in FIG. 137B, the SiNx layer 65is etched to the α-Si layer 72 in such a fashion as to leave only theportion of the channel protecting film. The n⁺ α-Si layer and theTi/Al/Ti layer corresponding to the data bus line, the source 41 and thedrain 42 are formed, and etching is then so made by patterning as toleave only the portions corresponding to the data bus line, the source41 and the drain 42. After the SiNx layer corresponding to the finalprotecting film 43 is formed as shown in FIG. 137D, etching is then madeto the surface of the glass substrate 17 in such a manner as to leavethe portions 43B and 40B corresponding to the portion necessary forinsulation and to the protrusions. At this time, the contact hole of thesource electrode 41 and the pixel electrode is formed simultaneously,too. Further, the ITO electrode layer is formed and patterned, therebyforming the pixel electrode 13. Therefore, the height of the protrusionis the sum of the SiNx layer 40 and the final protecting film 43.

FIG. 138 shows the structure of a modification of the panel of the 35thembodiment, and when the SiNx layer corresponding to the finalprotecting film 43 is etched, etching is made up to the upper surface ofthe SiNx layer 40. Therefore, the height of the protrusion is thethickness of the final protecting film 43.

FIGS. 139A to 139E show a process for manufacturing the TFT substrate ofthe panel of the 36th embodiment. As shown in FIG. 139A, the gateelectrode 31 is patterned on the glass substrate 17. Next, the ITOelectrode layer is formed and patterned to form the pixel electrode 13.The SiNx layer 40, the amorphous silicon (α-Si) layer 72 and the SiNx 65are serially formed as shown in FIG. 139B. Further, the SiNx layer 65 isetched up to the α-Si layer 72 in such a fashion as to leave only theportion of the channel protecting film. The n⁺ α-Si layer is furtherformed. As shown in FIG. 139C, etching is then made up to the surface ofthe pixel electrode 13 in such a fashion as to leave the necessaryportions and the portion 40B corresponding to the protrusion. TheTi/Al/Ti layer corresponding to the data bus line, the source 41 and thedrain 42 is formed as shown in FIG. 139D, and is then patterned in sucha fashion as to leave only the portions corresponding to the data busline, the source 41 and the drain 42. The n⁺ α-Si layer and the α-Si 72are etched by using the data bus line, the source 41 and the drain 42 asthe mask. After the SiNx layer corresponding to the final protectingfilm 43 is formed as shown in FIG. 139E, etching is made up to thesurface of the pixel electrode 13 in such a fashion as to leave theportion necessary for insulation and the portions 43B and 40Bcorresponding to the protrusions.

The explanation predetermined above explains the embodiments relating tothe manufacture of the protrusion 20B on the side of the TFT substrate17, but there are various modifications depending on the structure ofthe TFT substrate 17, and the like. In any case, the production cost canbe reduced by manufacturing the protrusion by conjointly using themanufacturing process of other portions of the TFT substrate 17.

As has been explained already, the protrusion of the dielectric materialdisposed on the electrode has the advantage that stable orientation canbe obtained because the direction of regulation of the orientation bythe slope coincides with the direction of regulation of the orientationby the electric field at the protrusion portion. However, the protrusionis the dielectric material disposed on the electrode and the alignmentfilm is formed on the protrusion. For this reason, the inside of theliquid crystal cell becomes asymmetric between a pair of electrodes, andthe charge is likely to stay with the application of the voltage. Inconsequence, the residual DC voltage becomes high, and the problem ofso-called “burn” occurs if the area of the projection is relativelylarge.

FIGS. 140A and 140B show the relationship between the thickness of thedielectric material on the electrode 120- and the residual DC voltage.FIG. 140A is a graph showing this relationship and FIG. 140B shows theportion corresponding to the thickness d of the dielectric material andthe position of the occurrence of “burn”. The vertical alignment film22, too, is the dielectric material, and the sum of the height of theprotrusion and the vertical alignment film 22 corresponds to thethickness d of the dielectric material as shown in FIG. 140B. Theresidual DC voltage increases with the increase of d as shown in FIG.140A. Therefore, burn is likely to occur at the portion of theprotrusion 20 shown in FIG. 140B. This also holds true of the case wherethe dielectric depression is formed on the electrode as in theeighteenth embodiment shown in FIG. 93. The 37th embodiment to beexplained next is directed to prevent the occurrence of such a problem.

FIGS. 141A and 141B show the structure of the protrusion in the 37thembodiment. FIG. 141A is a perspective view of the protrusion 20 andFIG. 141B is a sectional view. As shown in these drawings, theprotrusion 20 has a width of 7 μm, the width of its upper surface isabout 5 μm and its height is about 1 to 1.5 μm. A large number of finepores are formed on this upper surface, and each fine pore has adiameter of not greater than 2 μm.

FIGS. 142A to 142E are drawings showing a method of forming theprotrusion (on the side of the CF substrate) having such fine pores. Asshown in FIG. 142A, the glass substrate having the opposed electrode 12of the ITO film formed thereon is washed. A photosensitive resin(resist) is applied and is then baked to form a resist layer 351 asshown in FIG. 142B. A mask pattern 352 permitting light to transmitthrough the portions other than the protrusion and the pore portions isbrought into close contact with the resist layer 351 and then exposureis effected. The protrusion 20 shown in FIG. 142D is obtained by thencarrying out development. When baking is made further, the protrusion 20undergoes shrinkage, and the side surface changes to the slope as shownin FIG. 142E.

When the substrate having the fine pores formed in the protrusiondescribed above and the substrate not having the pores are assembled andthe residual DC voltage is measured by a flicker erasure method (DC: 3V, AC: 2.5 V, temperature: 50 C, DC application time: 10 minutes), theresidual DC voltage is 0.09 V when the fine pores are formed and is 0.25V when they are not formed. Because the residual DC voltage is reducedin this manner, seizure becomes more difficult to occur.

The liquid crystalline molecules are oriented perpendicularly to theslopes of the protrusions, etc, and to the electric field. It has beenfound out, however, when the gap of the protrusions becomes smaller tothe size approximate to the fine pores, the liquid crystalline moleculesare not oriented to the slope of the fine portions. Therefore, theliquid crystalline molecules are affected at the upper surface portionof the protrusions by the influences of the orientation due to theslopes on both sides and are oriented along this orientation.

FIG. 143 shows the protrusion structure of the 38th embodiment. In the38th embodiment, a groove having a width of 3 μm and a small thicknessis disposed below the protrusion 20B having a width of 7.5 μm on the TFTsubstrate side. Further, a chromic shading layer 34 is disposed belowthe protrusion 20B. Such a protrusion 20B can be manufactured by thesame method as that of the 37th embodiment. When the residual DC voltageis measured for the protrusion structure of the 38th embodiment, it is0.10V, and the result substantially equal to that of the 37th embodimentcan be obtained.

In the protrusion structure of the 38th embodiment, the liquidcrystalline molecules are not oriented at the groove portion in thedirection perpendicular to the substrate when no voltage is applied, andthe vertical orientation property gets deteriorated in some cases.However, because the shading film 34 is disposed, leaking light due toabnormal orientation at this portion is cut off and does not invite thedrop of the contrast.

Next, the shape of a section of a resist was examined. Normally, theresist has a section like the one shown in FIG. 144A immediately aftercompletion of patterning. However, in the mode of the present invention,a cylindrical section having a rather smooth slope contributes to morestable alignment. Substrates immediately after being patterned werebaked at 200° C., whereby the sectional shape of the resist was changedinto the one shown in FIG. 144B. FIGS. 145A to 145E are diagrams showinga change in sectional shape of the resist deriving from a change intemperature at which the patterned resist is baked. Even when the bakingtemperature was raised to 150° C. or more, a further change in sectionalshape was limited

Talking of the reasons why the resist was baked at 200° C., aside from areason that the sectional shape of the resist is intended to be changed,there is another important reason. That is to say, when the resistemployed in the prototypes is baked normally (at 135° C. for 40 min.),it is melted while reacting upon a solvent applied to an alignment film.In this embodiment, the resist is baked at a high enough temperaturebefore the alignment film is formed, and thus prevented from reactingupon the alignment film

In the first embodiment, the resist is baked at 200° C. in order to makethe sectional shape of the resist cylindrical. Data that has beendescribed so far was acquired using the pattern of protrusions whosesectional shape is cylindrical.

In the foregoing examples, the sectional shape of a resist is madecylindrical by optimizing the baking temperature. Depending on the linewidth of a resist, the resist becomes cylindrical naturally. FIGS. 146Ato 146C are diagrams showing the relationships between the line width ofa resist and the sectional shape thereof. When the line width is about 5micrometers, the resist has a preferable cylindrical shape naturally.Presumably, therefore, when the line width is about 7 micrometers orless, a resist having a naturally cylindrical sectional shape can beformed. In an existing display, the line width of 5 micrometers canactually be adopted. Depending on the performance of an exposure device,even when the line width is in the unit of submicrons, the samealignment can be thought to be attained in principle.

When a protrusion is used as the domain regulating means, furthermore,it becomes necessary to form a vertical alignment film thereon. FIGS.147A and 147B are sectional views of a conventional panel usingprotrusion as a domain regulating means, and illustrates the protrusion.Referring to FIG. 147A, on the substrates 16 and 17 are formed colorfilters and bus lines as well as ITO electrodes 12 and 13. Protrusions20A and 20B are formed thereon, and vertical alignment films 22 areformed on the ITO electrodes 12 and 13 that include the protrusions 20Aand 20B.

When the protrusion is formed by using the positive-type photoresistsuch as a TFT flattening agent HRC-135 manufactured by JSR Co. thesurface exhibits poor wettability to the vertical alignment film, expelsthe material of the vertical alignment film that is applied, and makesit difficult to form a vertical alignment film on the surface of theprotrusion. FIG. 147B shows this condition. Therefore, it causes aproblem in that no vertical alignment film 22 is formed on the surfacesof the protrusions 20A and 20B. The protrusions 20A and 20B having novertical alignment film 22 formed on the surfaces thereof, do not helpobtain a desired orientation. Therefore, light-leakage occurs from theprotrusions to deteriorate the quality of display. A 39th embodiment isto solve this problem.

According to the 39th embodiment, the surface of the protrusion istreated so that the material of the vertical alignment film easilyadheres onto the surface of the protrusion. As the treatment forenabling the material of the vertical alignment film to easily adhere tothe surface of the protrusion, it can be contrived to form fineruggedness on the surface of the protrusion so that the material of thealignment film can be favorably applied thereto, or the wettability ofthe surface of the protrusion can be enhanced relative to the materialof the vertical alignment film. When fine ruggedness is formed on thesurface of the protrusion, the liquid of the alignment film stays in theconcave portions, and the material of the alignment film is lessexpelled by the surface of the protrusion. The ruggedness can be formedby either a chemical treatment or a physical treatment. As the chemicaltreatment, ashing can be effectively employed.

FIGS. 148A to 148C are diagrams illustrating a method of formingprotrusions according to a 39th embodiment based on the ashingtreatment. Referring to FIG. 148A, a protrusion 20 is formed by usingthe photoresist on the electrode 13 (which, in this case, is a pixelelectrode 13 but may be an opposing electrode 12). The protrusion 20 hasthe shape of, for example, a stripe of a width of 10 μm and a height of1.5 μm. The protrusion is annealed to assume the shape of a dome incross section. The surface of protrusion on the substrate is subjectedto the ashing treatment using a conventional plasma asher. Through theplasma ashing, fine dents are formed on the surface of the protrusion asshown in FIG. 148B. The thus obtained substrate is washed, dried, andonto which a vertical orientation member is applied by using a printer.Due to the effect of ruggedness formed on the protrusion, theorientation member is not expelled, and a vertical alignment film isformed on the whole surface of the protrusion as shown in FIG. 148C.Thereafter, the processing is executed in the same manner as that of theordinary multi-domain VA system. The thus obtained liquid crystaldisplay device exhibits favorable display properties without defect thatstems from the expulsion of the alignment film.

Another example of the ashing treatment will be an ozone ashingtreatment exhibiting the same effect as that of the plasma ashingtreatment.

As a physical method of forming ruggedness, the substrate is washed witha brush by using a substrate washing machine after the protrusion hasbeen annealed. This forms ruggedness in the form of stripes on theprotrusion. Other examples of the method of physically formingruggedness include effecting the rubbing by using a rubbing device asshown in FIG. 149A, and transferring ruggedness of a roller 103 bypushing the rugged roller 103 onto the substrate on which the protrusion20 has been formed as shown in FIG. 149B.

FIG. 150 is a diagram illustrating the irradiation with ultraviolet raysin order to enhance the wettability of the surface of the protrusionrelative to the material of the vertical alignment film. As describedabove, a protrusion 20 same as that of FIG. 148C is formed on thesubstrate by using a photoresist. By using an excimer UV irradiationapparatus, the substrate is irradiated with ultraviolet rays of a mainwavelength of 172 nm in an environment in which an oxygen concentrationis not lower than 20% in a dosage of 1000 mJ/cm². This helps improve thewettability of the surfaces of the substrate and of the protrusionrelative to the material of the vertical alignment film. The thusobtained substrate is washed, dried, and is coated with the verticalorientation member by using a printer. Since wettability has beenimproved by the irradiation with ultraviolet rays, the orientationmaterial is not expelled, and the vertical alignment film is formed onthe whole surface of the protrusion. Thereafter, the processing iscarried out in the same manner as that of the ordinary multi-domain VAsystem. The thus obtained liquid crystal display device exhibitsfavorable display properties without defect that stems from theexpulsion of the alignment film.

FIGS. 151A and 151B are graphs illustrating a change in the expulsionfactor of the material of the vertical alignment film of when theconditions are changed in which the protrusion formed of a photoresistis irradiated with ultraviolet rays. FIG. 151A is a graph illustrating arelationship among the wavelength, dosage (radiation quantity) andexpulsion factor (repellent occurrence ratio). Ultraviolet rays having awavelength of not longer than 200 nm are effective. When the wavelengthis longer than 200 nm, the improvement is accomplished to only a smalldegree. When the ultraviolet rays have a wavelength of not longer than200 nm, furthermore, no expulsion (repellent) occurs with the dosage of1000 mJ/cm². FIG. 151B is a graph illustrating a relationship betweenthe oxygen concentration and the expulsion factor of when the protrusionis irradiated with ultraviolet rays having a wavelength of not longerthan 200 nm with a dosage of 1000 mJ/cm². In an environment where theoxygen concentration is low, ozone is not generated in sufficientamounts and the improvement is accomplished little. It is thereforedesired that the protrusion is irradiated with ultraviolet rays having awavelength of not longer than 200 nm in an environment in which anoxygen concentration is not lower than 20% with a dosage of not smallerthan 1000 mJ/cm².

As an apparatus for generating ultraviolet rays having a wavelength ofnot longer than 200 nm, there can be used a low-pressure mercury lamp inaddition to the above-mentioned excimer UV irradiation apparatus.

In the above-mentioned processing, the substrate was washed and driedafter irradiated with ultraviolet rays. However, the substrate may beirradiated with ultraviolet rays after it has been washed and dried. Inthis case, since the protrusion is irradiated with ultraviolet rays justprior to printing an alignment film thereon, wettability is not impairedby being left to stand after it is irradiated or by washing.

Repellence on the protrusion can be drastically improved if a silanecoupling agent, an alignment film solvent, etc, are applied before thealignment film is applied, and then the alignment film is formed. Moreconcretely, the substrate is baked (annealed) and the shape of theprotrusion is turned into the semicylindrical shape as shown in FIG.146. After this substrate is washed, hexamethyldisilane (HMDS) isapplied by using a spinner. A vertical orientation material is appliedto the substrate by using a printing press. In this way, the verticalalignment film is satisfactorily formed on the surface of theprotrusion. Incidentally, N-methylpyrrolidone (NMP) may be applied inplace of HMDS. Further, printing of the vertical alignment film may becarried but in a sealed NMP atmosphere and in this case, too, thevertical alignment film can be formed satisfactorily on the surface ofthe protrusion. Various solvents are available as the solvent to beapplied before the formation of the vertical alignment film, andgamma-butyrolactone, methyl cellosolve, etc, as the solvent of thealignment film can be used, for example.

FIGS. 152A to 152C are explanatory views useful for explaining anexample of the production method of the protrusion in the 39thembodiment, and represents an example wherein the protrusion is formedby a material dispersing therein fine particles (particulates) (exampleof the CF substrate side). As shown in FIG. 152A a positive typephotosensitive resin (resist) 355 containing 5 to 20% of fine aluminaparticles having a grain size of not greater than 0.5 μm in mixture isapplied onto the electrode 12. The resist 355 is exposed and developedby using a photomask 356 which shades the protrusion portion, as shownin FIG. 152B. After baking is carried out, a protrusion 20A shown inFIG. 152C can be obtained. The fine alumina particles 357 protrude fromthe surface of this protrusion 20A and fall off from the surface to formholes. In other words, fine concave-convexities are formed on thesurface of the protrusion 20A. For this reason, wettability can beimproved when the vertical alignment film is applied.

To increase the number of concave-convexities on the surface of theprotrusion in the embodiment described above, the proportion of the finealumina particles to be mixed with the resist must be increased. Whenthe proportion of the fine alumina particles exceeds 20%, however, thephotosensitivity of the resist drops and patterning can not be carriedout by exposure. FIGS. 153A to 153C show a method of manufacturing theprotrusion when the number of the concave-convexities on the surface ofthe protrusion must be increased.

A non-photosensitive resin containing a great proportion of fine aluminaparticles 357 having a grain size of not greater than 0.5 μm is appliedonto the electrode 12 as shown in FIG. 153A. Further, as shown in FIG.153B, a resist is applied to the surface of the resin, and exposure anddevelopment are carried out by using a photomask 358 shading theprotrusion portion. Because the resist remains at only the portionscorresponding to the photomask 358, the non-photosensitive resin atportions other than the protrusion portion is removed by etching. Whenbaking is carried out further, the protrusion 20A can be obtained asshown in FIG. 153C. The concave-convexities are formed similarly on thesurface of the protrusion 20A but because the proportion of the finealumina particles 357 mixed is great, a large number ofconcave-convexities are formed, and wettability can be much moreimproved than in the embodiment shown in FIG. 154 when the verticalalignment film is applied.

FIGS. 154A and 154B show another manufacturing method of theconcave-convexities on the surface of the protrusion by the fineparticles. In this example, after the resist 360 is applied to thesurface of the electrode 12, the fine alumina particles 361 are sprayedand allowed to adhere to the surface of the resist 360, followed then bypre-baking. Thereafter, the protrusion is patterned in the same way asin the prior art, and the protrusion 20A shown in FIG. 154B can beobtained. When this protrusion 20A is washed, the fine alumina particles361 exist on the surface of the protrusion 20A and fall off from thesurface to define the holes. In consequence, the concave-convexities areformed.

FIGS. 155A and 155B are explanatory views useful for explaining anexample of the manufacturing method of the protrusion in the 39thembodiment, and represents the example wherein a protrusion material isfoamed to form the concave-convexities on the surface of the protrusion.The resist for forming the protrusion 20 is first dissolved in a solventsuch as PGMEA (Propylene-Glycol MonoMethyl Ether Acetate), for example,is applied by a spinner and is then pre-baked (pre-cured) at 60° C.Under this state, large quantities of the solvent remain inside theresist. Patterning is then carried out by exposure and development byusing a mask.

According to the embodiments as described above, as shown in FIG. 156with a broken line, the temperature is gradually raised inside a cleanoven up to 200° C. in the course of 10 minutes, is held at thistemperature for longer than 75 minutes and is gradually returned to thenormal temperature in the course of 10 minutes. In contrast, accordingto this embodiment, as shown in FIG. 156 with a continuous line, thesubstrate is placed on a hot plate at 200° C. and is heated for 10minutes. At this time, about one minute time is necessary to raise thesubstrate temperature to 200° C. Thereafter, the substrate is leftstanding for cooling for 10 minutes to the normal temperature. Whenquick heating is carried out in this way, the solvent inside the resistis bumped and bubbles 362 are formed inside the resist as shown in FIG.155A. The bubbles 362 are emitted outside from the surface of theprotrusion 20 as shown in FIG. 155B. At this time, the traces 363 of thebubbles are left on the surface of the protrusion, forming thereby theconcave-convexities.

Incidentally, when the resist dissolved in the solvent is stirred beforethe application and the bubbles are introduced into the resist, foamingis more likely to occur than when the resist is quickly heated. Stirringmay be carried out while a nitrogen gas or a carbonic acid gas is beingintroduced. According to this method, the bubbles of the gas areintroduced into the resist and a part of the gas is dissolved in thesolvent, so that formability at the time of heating increases. Water ofcrystallization which emits water at about 120 to about 200° C. or aclathrate compound which emits a guest solvent may be mixed with theresist, too. Water is emitted from water of crystallization and changesto a steam or the guest solvent is emitted at the time of heating, andfoaming is more likely to occur. A solvent or a silica gel adsorbing agas may be mixed with the resist. The adsorbed solvent or the gas isemitted from the silica gel at the time of heating and consequently,foaming is more likely to occur. Incidentally, the solid material to bemixed must be smaller than the height of the protrusion and its width,and must be pulverized in advance to such a size.

The fine pores are formed in the protrusion in the 37th embodimentwhereas the grooves are disposed in the protrusion in the 38thembodiment, and according to such structures, the vertical alignmentfilm can be formed more easily on the surface of the protrusion. FIGS.157A to 157C show another method of forming the protrusion having thegrooves such as those of the 38th embodiment.

As shown in FIG. 157A, the protrusions 365 and 366 are formed adjacentto one another by using a photoresist which is used for forming amicro-lens. The patterning shape of this micro-lens can be changeddepending on the light reflection intensity, the baking temperature, thecomposition, and so forth, and when the suitable baking condition isset, the protrusion collapses and changes to the shape shown FIG. 157B.When the vertical alignment film 22 is applied to this shape, as shownin FIG. 157C, the vertical alignment film 22 can be formedsatisfactorily because the center of the protrusion 20 is recessed.After the material described above is applied to a thickness of 1.5 μm,the protrusions 365 and 266 are patterned to a width of 3 μm and a gapof 1 μm between the protrusions. The film is then baked at 180° C. for10 to 30 minutes. As a result, two protrusions are fused to each otherto form the shape shown in FIG. 157B. A desired shape can be obtained bycontrolling the baking time. The protrusions 365 and 266 can be fused toone another when the height is from 0.5 to 5 μm, the width is from 2 to10 μm and the gap is within the range of 0.5 to 5 μm. When the height ofthe protrusions is greater than 5 μm, this height affects the cellthickness (thickness of the liquid crystal layer) and impedes injectionof the liquid crystal. When the width of the protrusion is smaller than2 μm, on the other hand, the orientation limiting force of theprotrusion drops. Furthermore, when the gap between the protrusionsexceeds 5 μm, the two protrusions cannot be fused easily and when it issmaller than 0.5 μm, the depression can not be formed at the center.

In the foregoing was described the treatment for improving wattabilityof the protrusion relative to the material of the alignment filmaccording to the 39th embodiment. Here, the protrusion may have anypattern and may not be of the shape of a dome in cross section.Moreover, the material forming the protrusion is not limited to thephotoresist but may be of any material provided it is capable of forminga protrusion in a desired shape. By taking into consideration thechemical or physical formation of ruggedness in a subsequent process,however, it is desired to use a material which is soft, is not easilypeeled off and can be subjected to the ashing. The materials satisfyingthese conditions will be photoresist, black matrix resin, colored filterresin, overcoating resin and polyimide resin. These organic materialsmake it possible to improve (treat) the surfaces through the ashing orUV irradiation.

According to the 39th embodiment as described above, wettability of thesurface of the protrusion is improved for the material of the alignmentfilm, making it possible to prevent a trouble in that the alignment filmis not formed on the surface of the protrusion, the quality of displayis improved and the yield is improved.

In the past, a so-called black matrix is placed on the perimeter of eachpixel in order to prevent deterioration of contrast deriving fromleakage of light passing through a region between pixels. FIG. 458 is adiagram showing the structure of a panel of a prior art provided withblack matrices. As illustrated, a red filter 39R, green filter 39G, andblue filter 39B that coincide with red, green, and blue pixels areformed on a color filter (CF) substrate 16, and ITO electrodes 12 areformed on the CF substrate. Furthermore, black matrices 34 are formed onthe borders among the red, green, and blue pixels. Data bus lines andgate bus lines or TFT devices 33 are formed together with ITO electrodes13 on a TFT substrate 17. A liquid-crystal layer 3 is interposed betweenthe two substrates 16 and 17.

FIG. 159 is a diagram showing the structure of a panel of the 40thembodiment of the present invention, and FIG. 160 is a diagram showing apattern of protrusions over pixels in the 40th embodiment. Asillustrated, the red filter 39R, green filter 39G, and blue filter 39Bare formed on the CF substrate 16. As shown in FIG. 160, the protrusions20A for controlling alignment, which are included in the liquid crystalpanel of the first embodiment, are formed on the CF substrate 16, thoughthey are not shown in FIG. 159. The protrusions 20A are made of alight-interceptive material. Protrusions 61 are formed on the perimetersof pixels. The protrusions 61 are also made of a light-interceptivematerial and function as black matrices. The necessity of forming theblack matrices 34 like in the prior art is obviated. The protrusions 61functioning as black matrices can be formed concurrently with theprotrusions 20A. Using this process of manufacturing, the step ofcreating black matrices in the course of creating the CF substrate 16can be omitted. Reference numeral 62 denotes a TFT in each pixel. Theprotrusions 61 are designed to intercept light from the TFTs.

In FIG. 159, the protrusions 20A and 61 are formed on the CF substrate16. Alternatively, the protrusions 25-61 or 20A or both of them may beformed on the TFT substrate 17. Owing to this structure, a mismatchbetween the CF substrate 16 and TFT substrate 17 occurring duringbonding need not be taken into account. Consequently, the numericalaperture of the panel and the yield of a bonding step can be improvedoutstandingly. Assuming that the CF substrate 16 is provided with blackmatrices, when the ITO electrodes 13 on the TFT substrate 17 and openportions (portions without the black matrices) of the CF substrate 16are designed to be mutually identical, if a bonding mismatch occurred inthe process of manufacturing the panel, the mismatch region would causelight leakage. This disables normal display. Generally, even if ahigh-precision bonding machine is employed, a matching error of about ±5micrometers (μm) is present. A corresponding margin must therefore bepreserved. In consideration of the margin, an aperture for each blackmatrix is designed to be smaller. Thus, the above problem is coped with.That is to say, each black matrix is designed to invade into an ITOelectrode 13 formed on the TFT substrate 17 by about 5 to 10micrometers. When the protrusions 61 are formed on the TFT substrate 17,the panel is free from the adverse effect of the bonding mismatch.Consequently, the numerical aperture can be maximized. This advantagebecomes greater as each pixel of the panel gets smaller, that is, as aresolution improves. For example, in this embodiment, a substrate havingITO electrodes of pixels of which width is 80 micrometers and height is240 micrometers is employed. In any of the conventional modes, since amargin of 5 micrometers is needed, the width and length of the aperturebecome 70 micrometers and 230 micrometers respectively, and the area ofan aperture for each pixel becomes 16100 square micrometers. Bycontrast, in this embodiment, the area of the aperture for each pixel is19200 square micrometers. The numerical aperture is improved to beapproximately 1.2 times larger than the one permitted by theconventional mode. For realizing a display that offers twice as high aresolution as the one provided by the panel, the width and length of anelectrode are 40 micrometers and 120 micrometers respectively. In theconventional mode, the area of the aperture for each pixel is 3300square micrometers. In this embodiment, the area of the aperture foreach pixel is 4800 square micrometers and thus improved to beapproximately 1.5 times higher than the one permitted by theconventional mode. Thus, the higher the resolution is, the greater theadvantage is.

FIG. 161 is a diagram showing a pattern of a black matrix (BM) accordingto a 41th embodiment. It was described above that light leaks at thedomain regulating means. A minute domain having an orientation angle 90°different located at about the top of the protrusion can be used asdescribed above. The light leaks, however, unless a stable orientationcan be secured at about the top of the protrusion. For the contrast tobe improved, therefore, the domain regulating means is preferablymasked. One method of masking the protrusion is to form the protrusionof a light-shielding material. According to the 41th embodiment,however, the domain regulating means is masked by use of a black matrix(BM).

As described above, the BM 34 is used for shielding the leakage light atthe TFT and the boundary between the cell electrode and the bus line.The 41th embodiment, however, uses the BM also at the domain regulatingmeans. Consequently, the leakage light at the domain regulating meanscan be masked for an improved contrast.

FIG. 162 is a sectional view of a panel according to a 41st embodiment.As shown, the BMs 34 are arranged at positions corresponding to theprotrusions 20A, 20B, the TFT 33, and the interval between the bus lines(only the gate bus line 31 is shown) and the cell electrodes 13.

FIG. 163 shows a pixel pattern according to a 42nd embodiment.Conventionally, a delta arrangement is known, in which the displaypixels, which are substantially square in shape, are arranged inadjacent columns one half of a pitch displaced from each other. In acolor liquid crystal display device, a set of color pixels is configuredof three adjacent pixels of 13B, 13G, 13R. Each pixel is almost squarein shape, and as compared with a 1-to-3 rectangle, an equal proportionof liquid crystalline molecules can be easily secured in each directionof division without reducing the protrusion interval considerably. Insuch a case, the data bus line is extended in zigzag along theperimetric edge of the pixel. In this way, the delta arrangement is veryeffective in the case where a protrusion arrangement or a depressionarrangement is continuously formed over the entire substrate surface fororientation division.

The 43rd embodiment to be described next is an embodiment using theprotrusions for controlling alignment or the protrusions 61 serving asblack matrices in the 40th embodiment as spacers. As also shown in FIG.19, spacers are used to retain the distance (gap) between two substrates(thickness of cells) at a predetermined value. FIG. 164 is a diagramshowing the structure of a panel of a prior art, wherein spacers 45 areplaced on borders between pixels and define the thickness of cells. Thespacers 45 are, for example, spheres having a predetermined diameter.

FIGS. 165A and 165B are diagrams showing the structure of a panel of the43rd embodiment. FIG. 165A shows the structure of the panel of the 43rdembodiment, and FIG. 165B shows a modification. As shown in FIG. 165A,in the panel of the 43rd embodiment, protrusions 64 formed on theperimeters of pixels are made as thick as cells, and thus define thethickness of cells. In the drawing, the protrusions 64 are formed on theTFT substrate 17. Alternatively, the protrusions 64 may be formed on theCF substrate 16. This structure obviates the necessity of includingspacers. No liquid crystal is present at the positions of theprotrusions 64. For a vertically-aligned panel or the like, thepositions of protrusions (cell holder areas) of the panel appear inblack all the time irrespective of an applied voltage. The blackmatrices are therefore unnecessary, and the protrusions 64 need not bemade of a light-interceptive material but can be made of a transparentmaterial.

In the 43rd embodiment shown in FIG. 165A, the protrusions 64 define thethickness of cells. The precision in thickness of cells is dominated bythe precision in forming the protrusions, and is therefore poorer thanthat permitted when the spacers are used. A panel having the structureof the sixteenth embodiment was actually produced. As a result, a levelof uncertainty in thickness of cells can be controlled within ±0.1micrometers. This level would not pose any particular problem inpractice. However, this structure is unsuitable when the thickness ofcells must be controlled strictly. The modification shown in FIG. 167Bis a structure intended to solve this problem. In the modification shownin FIG. 167B, the spacers 45 are mixed in a resin to be made into theprotrusions 65, and the resin is applied to the substrate. The substrateis then patterned in order to form the protrusions. In thismodification, the merit of the 43rd embodiment that the spacers areunnecessary is lost, but there is a merit that the thickness of cellscan be defined irrespective to the precision in drawing a pattern ofprotrusions. A panel having the structure shown in FIG. 167B wasproduced actually. The thickness of cells could be defined so preciselythat an error falls within ±0.05 micrometers. Nevertheless, the spacersare still needed. However, since the spacers are mixed in a resin, thespacers are arranged while the resin is being applied. This obviates thenecessity of scattering the spacers at a panel production step. Thenumber of steps included in the process does not increase.

FIGS. 166A and 166B are diagrams showing another modifications of the43rd embodiment. FIG. 166A shows a structure in which the protrusions 64of the 43rd embodiment are replaced with protrusions 81 made of alight-interceptive material, and FIG. 166B shows a structure in whichthe protrusions 65 shown in FIG. 165B are replaced with protrusions 82made of a light-interceptive material. As mentioned above, in FIGS. 165Aand 165B, the protrusions 64 and 65 may be made of a transparentmaterial. The protrusions can still fill the role of black matrices.However, when the protrusions are made of the light-interceptivematerial, perfect light interception can be achieved.

FIG. 167 is a diagram showing a modification of the 43rd embodiment.Protrusions 83 are formed on the CF substrate 16 and protrusions 84 areformed on the TFT substrate 17. The protrusions 83 and 84 are broughtinto contact with each other, thus defining the thickness of cells. Aneffect exerted is the same as the one exerted by the 43rd embodiment andits modification.

In the 43rd embodiment and its modification, protrusions lying on theperimeters of pixels are used to define the thickness of cells.Protrusions for controlling alignment, for example, the protrusions 20Ashown in FIG. 160 may be used to define the thickness of cells.

Furthermore, in the 40th embodiment, 43rd embodiment, and modificationsof the 43rd embodiment, protrusions are formed all over the perimetersof pixels. Alternatively, the protrusions may be formed on parts of theperimeters of the pixels. For example, the protrusions 61, 64 and 81 to84 in the 43rd embodiment and its modification may be made of alight-interceptive material and formed along one sides of only TFTportions of pixels, that is, portions 62 shown in FIG. 59. As mentionedabove, as far as a so-called normally black-mode panel that, like avertically-aligned (VA) panel, appears in black when no voltage isapplied to ITO electrodes is concerned, even if the black matrices areexcluded, light leakage hardly poses a problem. In this embodiment,therefore, only the TFT portions of pixels are coated with alight-interceptive resin but the drain bus lines and gate bus linessurrounding the pixels are not coated therewith. As mentioned above, asthe number of light-interceptive regions decreases, the numericalaperture improves accordingly. This is advantageous. The structure inwhich protrusions are formed along only the TFT portions can be adaptedto the 43rd embodiment and its modifications shown in FIGS. 165A to 169.

In the 43rd embodiment, the black matrix is provided with the functionof the spacer but according to the prior art, spherical spacers having adiameter equal to the cell thickness are sprayed on one of thesubstrates having the vertical alignment film formed thereon and thenthe other substrate is bonded. When the protrusion is formed on theelectrode, however, a part of the spacers so sprayed is positioned onthe protrusion. if the diameter of the spacers is equal to the cellthickness in the case where no protrusion is formed, the cell thicknessbecomes greater than the desired thickness due to the existence of thespacer on the protrusion. Further, when any force is applied fromoutside to the panel that is once assembled and the spacers move on theprotrusion, the cell thickness becomes greater at that portion and theproblem of non-uniform display develops. The forty-fourth embodiment tobe next explained is directed to solve this problem by decreasing thediameter of the spacers in consideration of the thickness of theprotrusion.

FIGS. 168A to 168C show the panel structure of the 44th embodiment. FIG.168A shows the TFT substrate 17 before assembly, FIG. 168B shows the CFsubstrate 16 before assembly and FIG. 168C shows the assembled state. Asshown in FIGS. 168A and 168B, the protrusion 20A is formed on theelectrode 12 of the CF substrate 16 and the vertical alignment film 22is further formed. The protrusion 20B is formed on the electrode 13 ofthe TFT substrate 17 and the vertical alignment film 22 is beforeassembly and further formed. The protrusions 20A and 20B have the sameheight of 1 μm and are assembled so that they do not cross mutually whenviewed from the panel surface. The cell thickness is 4 micrometers (μm),and the diameter of the spacer 85 made of a plastic material is 3 μmwhich is the balance obtained by subtracting the height of theprotrusion from the cell 163 A thickness. As shown in FIG. 168A, 150 to300 pcs/mm² of spacers 85 are sprayed (sprinkled) on the TFT substrate17. A seal is formed from a bonding resin on the CF substrate 16 and theCF substrate 16 is bonded to the TFT-substrate 17. The spacers 85 arepositioned on the protrusions 20B or below the protrusions 20A at acertain probability as shown in FIG. 168C. This probability correspondsto the proportion of the areas of the protrusions 20A and 20B to theentire area. Under the state shown in FIG. 168C, the cell thickness islimited by the spacers positioned on the protrusions 20B or below theprotrusions A and the thickness of the protrusions. The spacers 45existing at portions other than the protrusions 20A and 20B are floatingspacers that do not affect the cell thickness. Since the cell thicknessis limited by the protrusions 20A and 20B, the cell thickness hardlyexceeds the desired value. Even when the spacers at portions other thanthe portions of the protrusions move to the protrusion portions duringthe use of the panel, the cell thickness does not become thick, and evenwhen the spacers existing at the protrusion portions move to theportions other than the protrusion portions, they change to only thefloating spacers.

FIG. 169 is a graph showing the relationship between the scattered(sprinkle) density of the spacers and the cell thickness. When thescattered density of the spacers is 100 to 500 pcs/mm² the cellthickness falls within the range of 4 μm±0.5 μm.

Next, FIG. 172 shows the experimental result of variance of the cellthickness that occurs when a force is applied from outside to the panel,and the scattered density of the spacers. It can be appreciated fromthis result that when the scattered density is lower than 150 pcs/mm²,variance is likely to occur again t the force applied, and when thescattered density exceeds 300 pcs/mm², variance is likely to occuragainst the tensile force. Therefore, the optimum scattered density is150 to 300 pcs/mm².

In the manufacturing process of the liquid crystal display panel, ionicimpurities are sometimes entrapped and ions contained in the liquidcrystal and ions eluting from the alignment film, the protrusion formingmaterial, the seal material, etc, mix in the liquid crystal panel insome cases. When the ions mix into the liquid crystal panel, thespecific resistance of the panel drops, so that the effective voltageapplied to the panel drops, too, thereby resulting in burn of thedisplay and in the drop of the voltage retention ratio. In this way,mixing of the ions into the panel lowers display performance andreliability of the liquid crystal panel.

For these reasons, the ion adsorption-capacity is preferably provided tothe dielectric protrusion formed on the electrode, used as the domainregulating means in the embodiments described above. There are twomethods of providing the ion adsorption capacity to the protrusion. Thefirst method irradiates the ultra-violet rays and the second adds amaterial having the ion adsorption capacity to the material of theprotrusion.

Surface energy of the protrusion forming material rises when theultra-violet rays are irradiated to the material. Consequently, the ionadsorption capacity can be improved. The surface energy γ can beexpressed by the sum of the polarity term γp of the surface energy andits scatter term γd. The polarity term is based on the Coulombelectrostatic force and the scatter term, on the scatter force among thevan der Waals force. When the ultra-violet rays are irradiated, bondingat portions having a low bonding energy is cut off, and oxygen in aircombines with the cut portions. Accordingly, the polarizability of thesurface increases, the polarity term becomes great and the surfaceenergy increases. When the degree of polarization increases, the ionsbecome more likely to be adsorbed to the surface. In other words, thesurface of the protrusion comes to possess the ion adsorption capacitywhen the ultra-violet rays are irradiated. It is preferred toselectively irradiate the ultra-violet rays to only the protrusions whenirradiating the ultra-violet rays, but because the bonds of theprotrusion forming material are more likely to be cut off than the bondson the surface of the substrates, only the protrusions come to possessthe ion adsorption capacity even when the ultra-violet rays areirradiated to the entire surface of the panel. The vertical alignmentfilm is formed after the ultra-violet rays are irradiated.

An ion exchange resin, a chelating agent, a silane coupling agent, asilica gel, alumina, zeolite, etc, are known as the materials having theion adsorption capacity. Among them, the ion exchange resin exchangesthe ions, and supplements the ions that have existed as impurities fromthe beginning. Instead, it discharges other ions and for these reasons,it is not suitable for the protrusion forming material. Among thematerials having the ion supplementing capacity, some materials existwhich have the ion supplementing capacity without emitting thesubstituent ions, and such materials are preferably used. Examples ofsuch materials are crown ether having the chemical formula shown inFIGS. 171A and 171B and krypt and having the chemical formula shown inFIGS. 172A and 172B. Further, inorganic materials such as alumina andzeolite have the capacity of supplementing ions without emitting ions.Therefore, these materials are used. Incidentally, since the kinds ofthe ions adsorbed by one ion adsorption material are limited, materialsadsorbing different ions are preferably used in combination.

A protrusion line having a width of 7.5 μm, a height of 1.5 μm and a gapof 15 μm between the protrusions is formed from a positive type resist,and is subjected to the treatment for imparting the various ionadsorption capacity described above so as to manufacture the panels.FIG. 250 shows the result of measurement of the initial ion density andthe ion density (unit: pc) after the use for 200 hours of the panel somanufactured. In FIG. 250, ultra-violet rays of 1,500 mJ are irradiatedin Example C, 0.5 wt % of crown ether is added in Example D, zeolite isadded in Example E, and crown ether and zeolite are added in Example F.For reference, the case where the treatment for imparting the ionadsorption capacity is not carried out is represented as ComparativeExample. A 10 V triangular wave having a frequency of 0.1 Hz is appliedat the time of use, and the temperature at the time of measurement is50° C. It can be appreciated from the result that the initial value ofthe ion density remains at substantially the same level regardless ofthe ion adsorption capacity treatment. However, the ion density after200 hours drastically increases when this treatment is not carried out,but when the treatment is carried out, the increase remains small.

When the sample to which the ultra-violet rays are irradiated and thesample which is not at all treated are subjected to the practicalrunning test, burn occurs in the un-treated sample but does not occur inthe sample subjected to the ultra-violet irradiation.

In the 40th embodiment, the structure in which a pattern of protrusionsis drawn on the CF substrate 16 using black matrices has been disclosed.The structure will be described below.

As mentioned above, if a pattern of protrusions can be drawn on the CFsubstrate 16 in the conventional manufacturing process, since a new stepneed not be added, an increase in cost deriving from drawing of apattern of protrusion can be minimized. The seventeenth embodiment is anembodiment in which a pattern of protrusions are drawn on the CFsubstrate 16 by utilizing the conventional manufacturing process.

FIGS. 173A and 173B are diagrams showing the structure of the CFsubstrate of the 45th embodiment. As shown in FIG. 173A, in the 45thembodiment, the color filter (CF) resins 39R and 39G (and 39B) areapplied pixel by pixel to the CF substrate 16. Black matrices or anappropriate material such as a CF resin or any other flattening resin isused to define a pattern of protrusions 50A by tracing predeterminedpositions. ITO (transparent) electrodes 12 are then formed on thepattern of protrusions. A material to be made into the black matricis isnot restricted to any specific one. For forming protrusions, however, acertain thickness is needed. From this viewpoint, the adoption of aresin is preferable.

FIG. 173B is a diagram showing a modification of the CF substrate in the45th embodiment. Black matrices or an appropriate material such as a CFresin or any other flattening resin is used to draw a pattern ofprotrusions 50B by tracing predetermined positions on the CF substrate16. Thereafter, the CF resins 39R and 39G are applied. Consequently, theCF resin defining the pattern of protrusions gets thicker. The patternof protrusions can now provide protrusions as it is. The ITO(transparent) electrodes 12 are then formed.

According to the structure of the 45th embodiment, protrusions can beformed at any positions on the CF substrate.

FIG. 174 is a diagram showing the structure of a panel of the 46thembodiment. In the 46th embodiment, the protrusions 50 are formed on theperimeters of pixels on the CF substrate 16, that is, on seams betweenthe CF resins 39R, 39G, and 39B or on seams relative to black matrices34. On the TFT substrate 17, the protrusions 20B are formed at positionscoincident with intermediate positions between the seams. For formingcontinuous protrusions along one sides of the pixels opposed to theseams on the CF substrate 16, that is, for drawing a pattern of linearprotrusions, a pattern of linear protrusions is drawn parallel to thepattern of protrusions by tracing positions near the centers of thepixels on the TFT substrate. Moreover, when continuous protrusions areformed along all sides of the seams between the pixels on the CFsubstrate 16, the pattern shown in FIGS. 80A to 81 is drawn. On the TFTsubstrate 17, pyramidal protrusions are formed near the centers of thepixels.

The structure of the panel of the 46th embodiment can be adapted tovarious forms. An example of the structure of the CF substrate of the46th embodiment will be described below.

FIG. 175A to 180B are diagrams showing examples of the structure of theCF substrate of the 46th embodiment. FIG. 175A shows a structure inwhich the black matrix (BM) 34 is interposed between each pair of the CFresins 39R and 39G. The black matrices 34 are formed thicker than the CFresins, and the ITO electrodes 12 are formed on the black matrices 34.The black matrices 34 become protrusions. Even in this case, the blackmatrices 34 should preferably be made of a resin or the like.

In FIG. 175B, the thin black matrices 34 made of a metal or the like areformed on the CF substrate 12. The CF resins 39R and 39G are applied tothe black matrices, thus forming color filters. Thereafter, the CF-resin39 is applied in order to form protrusions 70. The ITO electrodes 12 areformed on the protrusions.

In FIG. 176A, the thin black matrices made of a metal or the like areformed on the CF substrate 12. The CF resins 39R and 39G are applied tothe substrate, thus forming color filters. A resin other than the CFresin, for example, a resin used as a flattening material is used toform protrusions 71 without the use of the black matrices 34. The ITOelectrodes 12 are then formed on the protrusions. In this case, like thestructure shown in FIG. 175A, the flattening material is applied thickerthan the CF resin.

In FIG. 176B, a resin or the like is used to form the black matrices 34,of which thickness is the same as the thickness of protrusions, on theCF substrate 12. The CF resins 39R and 39G are applied so that they willoverlap the black matrices 34, thus forming color filters. Thereafter,the ITO electrodes 12 are formed. The portions of the CF resinsoverlapping the black matrices 34 serve as protrusions.

In FIG. 177A, the thin black matrices 34 made of a metal or the like areformed on the CF substrate 12, and the CF resin 39R is then applied tothe substrate. Thereafter, the CF resin 39G is applied to overlap the CFresin 39R, and the ITO electrodes 12 are then formed. Portions of the CFresin 39G overlapping the CF resin 39R serve as protrusions. At thepositions of the protrusions, the black matrices 34 are included for notallowing passage of light. Either of the color filter resins may overlapthe other color filter resin. According to this structure, protrusionscan be formed at the step of forming color filters. The number of stepswill therefore not increase.

In FIG. 177B, a flattening material 71 is applied to overlap parts ofthe CF resins 39R and 39G on the same substrate as the one shown in FIG.176A. Portions of the flattening material 71 overlapping the CF resinsserve as protrusions. Owing to this structure, the flattening material71 can be made as thin as the height of protrusions.

The aforesaid structures are structures in which ITO electrodes areformed on protrusions and electrodes have the protrusions. Next, anexample of a structure in which an insulating material is used to formprotrusions on the ITO electrodes will be described.

In FIG. 178, after color filters are formed on the CF substrate 16 byapplying the CF resins 39R and 39G, the ITO electrodes 12 are formed.The black matrices 34 are then placed in order to form protrusions. Evenin this case, the number of steps will not increase.

In FIG. 179A, after the thin black matrices 34 are formed on the CFsubstrate 16, the ITO electrodes 12 are formed. Color filters are thenformed by applying the CF resins 39R and 39G. At this time, the CF resin39G is applied to overlap the CF resin 39R, thus forming protrusions.Even in this case, the number of steps will not increase.

In FIG. 179B, after the thin black matrices 34 are formed on the CFsubstrate 16, color filters are formed by applying the CF resins 39R and39G. The ITO electrodes 12 are then formed. The flattening material 71is then used to form protrusions.

In FIG. 180A, after the ITO electrodes 12 are formed on the CF substrate16, color filters are formed by applying the CF resins 39R and 39G. Theblack matrices 34 are then placed on the color filters, thus formingprotrusions.

In FIG. 180B, after the thin black matrices 34 are formed on the CFsubstrate 16, color filters are formed by applying the CF resins 39R and39G. A flattening material 72 is used to flatten the surface. The ITOelectrodes 12 are then formed on the surface and the black matrices 34are further formed, whereby protrusions are realized.

FIGS. 181A to 181G are diagrams illustrating the steps for producing thecolor filter (CF) substrate according to a 47th embodiment. The CFsubstrate has a protrusion as a domain regulating means.

Referring to FIG. 181A, a glass substrate 16 is prepared. Then, as shownin FIG. 181B, a resin (resin B, CB-7001, manufactured by Fuji Hanto Co.)39B′ for negative-type flue filter is applied onto the glass substrate16 maintaining a thickness of 1.3 μm. Then, as shown in FIG. 181C, theresin B is formed on the portions of the blue (B) pixel, BM portion andprotrusion 20A by the photolithography method using a photomask 370 asshown. Next, referring to FIG. 181D, a resin (resin R, CR-7001,manufactured by Fuji Hanto Co.) 39R′ for red filter is applied to formthe resin R on the portions of the red (R) pixel, BM portion andprotrusion 20A by the photolithography method. Referring to FIG. 181E, aresin (resin G, CG-7001, manufactured by Fuji Hanto Co.) 39G′ for greenfilter is applied to form the resin G on the portions of the green (G)pixel, BM portion and protrusion 20A by the photolithography method.Through the above-mentioned steps, corresponding color filter (CF)layers are formed in one layer only on the pixel portions B, G and R,and the resins B, G and R are formed in three layers being superposedone upon the other on the BM portion and on the protrusion 20A. Theportions where the resins B, G and R are superposed in three layers areblack portions without almost permitting the passage of light.

Next, a transparent flattening resin (HP-1009 manufactured by HitachiKasei Co.) is applied by a spin coater maintaining a thickness of about1.5 μm, post-baked in an oven heated at 230° C. for one hour, and an ITOfilm is formed by mask-sputtering. Referring next to FIG. 181F, a blackpositive-type resist (CFPR-BKP manufactured by Tokyo Ohka Co.) isapplied by the spin coater maintaining a thickness of about 1.0 to−1.5μ, pre-baked, and is exposed to ultraviolet rays having a wavelengthof 365 nm in a dosage of 1000 mJ/cm² from the back surface of the glasssubstrate 16 through the CF resin. The portions where the resins B, Gand R are superposed in three layers permit ultraviolet rays to transmitthrough less than through other portions, and where a threshold value ofexposure is not reached. When developed with an alkali developingsolution, the BM portion 34 and the protrusion 20A are formed that werenot exposed to light, and are post-baked in an oven heated at 230° C.for one hour. Moreover, a vertical alignment film 22 is formed tocomplete the CF substrate.

FIG. 182 is a sectional view of a liquid crystal panel completed bysticking the CF substrate 16 prepared as described above and a TFTsubstrate 17 together. In the TFT substrate 17, a slit 21 is formed as adomain regulating means in the pixel electrode 13, and a verticalalignment film 22 is formed thereon. Reference numeral 40 denotes a gateprotection film and a channel protection film. On the portions where thelight must be shielded, the BM 34 and the resins of the three layers B,G and R are superposed one upon the other to favorably shield the light.The protrusion 20A of the CF substrate 16 and the slit 21 in the TFTsubstrate 17 divide the orientation of liquid crystals making itpossible to obtain good viewing angle characteristics and high operationspeed.

According to the 47th embodiment as described above, the protrusion 20Awhich is the domain regulating means and the BM 34 are formed on the CFsubstrate without the need of exposure to light through a pattern, butby patterning by exposure to light from the back surface, making itpossible to simplify the steps for forming the protrusion 20A and the BM34, to lower the cost and to increase the yield.

In the 47th embodiment, the pigment scatter method is employed forforming the CF. This can be similarly adapted even to the dying methodand to the case where a non-photosensitive resist formed by dispersing apigment in the polyimide is to be formed by etching. According to the47th embodiment, the CF resins are superposed in three layers on theportions of the protrusion 20A and BM 34. These resins, however, may besuperposed in two layers provided the wavelength of the irradiationlight and the irradiation energy are suitably selected at the time ofexposure through the back surface.

In the 47th embodiment, the BM and the protrusion which is the domainregulating means are formed on the CF substrate without patterning.However, the fifth embodiment can be also adapted even to the case wherethe BM only is formed without forming protrusion, as a matter of course.A 48th embodiment deals with a case where the BM is formed but formingthe protrusion by a method different from that of the 47th embodiment.

FIGS. 183A and 183B are diagrams illustrating a step of producing the CFsubstrate according to the 48th embodiment, and FIGS. 184A and 184B arediagrams illustrating a panel structure according to the 48thembodiment.

In the 48th embodiment, no CF resin is superposed on a portioncorresponding to the protrusion but the CF resin is superposed on aportion corresponding to the BM only to form a BM protrusion 381. Next,without effecting the flattening, an ITO film 12 is formed as shown inFIG. 183A, and the above-mentioned black positive-type resist 380 isapplied thereon maintaining a predetermined thickness, for example,about 2.0 μm to 2.5 μm. Then, the developing is effected by exposure tolight from the back surface to obtain a panel having a BM resist 380superposed on the BM protrusion 381 as shown in FIG. 183B. The BM 34 isconstituted by both the BM protrusion 381 and the BM resist 380.

The CF substrate and the TFT substrate are stuck together to prepare apanel shown in FIG. 184A. FIG. 184B is a view illustrating, on anenlarged scale. A circular portion of a dotted line of FIG. 184A, and inwhich the BM resist 380 is in contact with the TFT substrate 17, and thedistance between the substrates is defined by both the BM protrusion 381and the BM resist 380. That is, the BM protrusion 381 and the BM resist380 work as a spacer.

According to the 48th embodiment as described above, there is no need topattern the BM simplifying the steps, and the BM works as a spacereliminating the need of providing the spacer. In the 48th embodiment,the positive-type resist was used to form the BM by exposure to lightthrough the back surface without effecting the patterning. However,either the negative-type resist or the positive-type resist can be usedprovided it can be patterned by the photolithography method. The resistwhich is not of a black color can be used for forming protrusion whichworks as a domain regulating means, or can be used as a spacer incompliance with the 47th embodiment.

Next, described below is a case where the protrusion 341 on which the CFresin is superposed in the 48th embodiment, is directly used as the BM.

FIGS. 185A to 185C are diagrams for illustrating the steps for producingthe CF substrate according to a 49th embodiment, and FIG. 186 is adiagram illustrating a panel structure according to the 49th embodiment.

Referring to FIG. 185A, the CF resin is superposed in three layers onthe BM to form a protrusion 381 which permits light to pass through verylittle. Referring next to FIG. 185B, the above-mentioned transparentflattening resin is applied by a spin coater maintaining a thickness ofabout 1.5 μm, post-baked at 230° C. for one hour and, then, an ITO film12 is formed. Then, in FIG. 185C, a positive-type resist (SC-1811manufactured by Shipley Far East Co.) is applied maintaining a thicknessof about 1.0 to 1.5 μm), pre-baked, and a protrusion 20A is formed bythe photolithography method. The protrusion 381 formed by superposingthe CF resins B, G and R in three layers does not almost permit light topass through and works as the BM. The thus completed CF substrate 16 andthe TFT substrate 17 are stuck together via a spacer 45 to obtain apanel as shown in FIG. 186.

The 47th to 49th embodiments have dealt with the cases where the BM wasformed by superposing the CF resins. The liquid crystal display deviceof the VA system holding the negative-type liquid crystals, is normallyblack, and the non-pixel portions to where no voltage is applied do notalmost permit light to pass through. Therefore, the BM for shieldinglight for the non-pixel portions may have a light transmission factorwhich is not acceptable in the case of the normally white device. Thatis, the BM may have a light transmission factor which is low to someextent. An 50th embodiment is to easily produce the CF substrate bygiving attention to this point, and uses a CF resin or, concretelyspeaking, uses the resin B as the BM. This does not develop any problemfrom the standpoint of quality of display.

FIG. 187 is a diagram illustrating a step for producing the CF substrateaccording to the 50th embodiment, and FIGS. 188A and 188B are diagramsillustrating the panel structure according to the 50th embodiment.

Referring to FIG. 187, the CF resins R, G (CR-7001, CG-7001,manufactured by Fuji Hanto Co.) of two colors are formed on the glasssubstrate 16, and the negative-type photosensitive resin B (CB-7001manufactured by Fuji Hanto Co.) is applied thereon by using a spincoater or a roll coater and is pre-baked. Then, the glass substrate 16is exposed to ultraviolet rays of a wavelength of 365 nm in a dosage of300 mJ/cm² from the back surface thereof, developed by using an alkalideveloping solution (CD manufactured by Fuji Hanto Co.), and ispost-baked in an oven heated at 230° C. for one hour. Thereafter, an ITOfilm is formed and, then, a vertical alignment film is formed. That is,the resin B is formed on the portions other than the portions where theCF resins R and G are formed. The CF resins are not formed on theportions where the light must be shielded by forming the BM; i.e., theresin B is formed on the portions where the light must be shielded.

Referring to FIG. 188A, the resin B 39B is formed as BM on the portionsof bus lines 31, 32 and on the portions of TFTs where the light must beshielded. FIG. 188B is a diagram illustrating, on an enlarged scale, acircular portion of a dotted line of FIG. 188A. As shown, a highnumerical aperture can be obtained by selecting the width of thelight-shielding portion (resin B) 382 of the side of the CF indicated byan arrow to be equal to the widths of the bus lines 31, 32 of the TFTsubstrate 17 to which a margin {circle around (1)} is added at the timeof sticking the two pieces of substrates together.

In the 50th embodiment, the resin B is formed last since thetransmission factors of the g-, h- and i-rays of photosensitivewavelengths are resin B>resin R>resin G. When the CF resin having a highexposure sensitivity (which may be exposed to a small amount of light)and the CF resin which permits photosensitizing wavelength to passthrough at a large rate, are formed last, the resin of a color formedlast remains little on the resins that have been formed already, whichis desirable.

In general, it is effective if the first color is that of a resin(generally B>R>G in the transmission light) which makes it easy todiscriminate the position alignment mark of an exposure device, and ifthe alignment mark is formed together with the pixel pattern.

FIG. 192 is a diagram illustrating the structure of the CF substrateaccording to a 51th embodiment. In the conventional liquid crystaldisplay device, the BM 34 of metal film is formed on the glass substrate16, the CF resin is formed thereon, and the ITO film is further formedthereon. According to the ninth embodiment, on the other hand, the BM isformed on the ITO film.

In the 51th embodiment, the CF resin 39 is formed by patterning on theglass substrate 16 like in the embodiments described above. As required,a transparent flattening member may be applied thereon. Next, atransparent ITO film 12 is formed, and a light-shielding film 383 isformed on a diagramed portion thereon. For example, the ITO film 12 isformed by sputtering maintaining a thickness of about 0.1 μm via a mask,and chromium is grown thereon as a light-shielding layer maintaining athickness of about 0.1 μm. Furthermore, a resist is uniformly appliedonto the light-shielding layer maintaining a thickness of about 1.5 μmby such a coating method as spin coating, and the light-shielding filmis exposed to light through a pattern, developed, etched, and is peeled,thereby to form the light-shielding film 383. The light-shielding film383 is composed of chromium and is electrically conducting, has a largecontact area relative to the ITO film 12 and makes it possible to lowerthe resistance of the ITO film 12 over the whole substrate. The ITO film12 and the light-shielding film 383 may be formed by any method.According to the conventional method, the ITO film 12 is formed, and thesubstrate is annealed and is washed to form the chromium film. Accordingto the 51th 20 embodiment, the ITO film 12 and the chromium film arecontinuously formed in an apparatus, making it possible to decrease thestep of washing and, hence, to simplify the steps. Therefore, nofilm-forming device is required, and the apparatus is realized in asmall size.

FIGS. 190A and 190B are diagrams illustrating a modified example of theCF substrate of the 51th embodiment. In FIG. 190A, the three CF resinsare formed, another resin 384 is formed in a groove in the boundary ofthe CF resins, and the ITO film 12 and the light-shielding film 383 areformed. In FIG. 190B, the two CF resins 39R and 39G are formed like inthe eighth embodiment explained with reference to FIG. 187. Then, theresin B is applied maintaining a thickness of about 1.5 μm, and thesubstrate is exposed to light from the back surface thereof and isdeveloped to form a flat surface. Then, the ITO film 12 and thelight-shielding film 383 are formed thereon. Since the surfaces of theCF layers are flat, the ITO film is not cut, and the resistance of theITO film 12 can be lowered over the whole substrate.

When a colored resin having a low reflection factor is used as the resin384 or 39B under the light-shielding film 383, the light-shieldingportion exhibits a decreased reflection factor, and light falling on theliquid crystal display device from the outer side is less reflected.Furthermore, when a colored resin having a small transmission factor isused as the resin 384 or 39B under the light-shielding film 383, thelight-shielding portion exhibits a decreased transmission factor,enabling the contrast of the liquid crystal display device to beenhanced.

In the structure of FIG. 190B, furthermore, the CF resin 34B is formedrequiring no patterning. Therefore, there is no need to use an exposureapparatus which is capable of effecting the patterning and is expensivecorrespondingly, and the investment for the facilities can be decreasedand the cost can be decreased, too.

FIG. 191 is a diagram illustrating a modified example of the 51stembodiment. Spacer for controlling the thickness of the liquid crystallayer are mixed in advance in the resist that is to be applied onto thelight-shielding film. After the resist is patterned, therefore, thespacers 45 are formed on the light-shielding film that is formed in anyshape. This eliminates the step for dispersing the spacers.

FIG. 192 is a diagram illustrating a CF substrate according to a 52rdembodiment. According to this embodiment, a chromium film is formed onthe ITO film 12 and a resist is applied thereon. At the time when thelight-shielding film 383 is to be patterned and exposed to light, theprotrusion that works as a domain regulating means is patternedsimultaneously therewith. After developing and etching, the resist isnot peeled off but is allowed to stay. Thus, an insulating protrusion387 that works as a domain regulating means is formed on the CFsubstrate 16. By using such a CF substrate, there is realized a panel ofa structure shown in FIG. 193.

As described in the 47th embodiment, CF films are formed on a CFsubstrate, the CF substrate is coated with flatting resin such asacrylic resin so that the surface of the substrate becomes flat, and anelectrode of an ITO film is formed thereon. In some cases, the surfaceflatting step is omitted in order to simplify the process. The CFsubstrate to which the surface flatting step is not performed is calleda CF substrate with no top-coat. The CF substrate with no top-coat hasgrooves formed between respective CF films. The ITO film is formed witha sputtering process. When the ITO film is formed is formed on the CFsubstrate with no top-coat, it occurs a problem that the ITO layer isrigid on flat surfaces but it is coarse at the grooves because thesputtering process has anisotropy.

Therefore, when material of vertical alignment film is coated orprinted, solvent included in the material infiltrates into the CF filmsthrough the grooves after the coating or printing to a precuringprocess. The infiltrated solvent remains inside the CF layers after theprecuring process is completed. The solvent remained inside the CF filmsgenerates craters on the surfaces of the vertical alignment film. Thecraters cause display unevennesses. According to the 51th embodiment,the light-shielding film provided at the grooves can prevents theinfiltration of solvent. In a 52th embodiment, resin provided at thegrooves between respective CF films are used as protrusions.

FIGS. 251A to 251D are diagrams showing a production process of a CFsubstrate of the 52th embodiment. FIG. 251A shows a CF substrate with notop-coat. The CF films 39R, 39G and 39B are formed, the light-shieldingfilms 34 are formed under the boundaries of the respective CF films, andthe ITO film is formed the CF films. As shown in FIG. 251B, a positiveresist is coated. As shown in FIG. 251C, the positive resist isirradiated with ultraviolet light from a surface of the glass substrate,and it is developed. Then, protrusions 390 are formed at positionscorresponding to the light-shielding films 34. The protrusions 390prevent the infiltration of solvent. Further, the protrusions 390operate as the protrusions 20A of the CF substrate.

The structures of a liquid crystal display in accordance with thepresent invention have been described so far. Examples of applicationsof the liquid crystal display will be described below.

FIG. 194 shows an example of a product employing the liquid crystaldisplay in accordance with the present invention, and FIG. 195 is adiagram showing the structure of the product. As shown in FIG. 195, aliquid-crystal panel 100 has a display surface 111, and makes itpossible to view a displayed image not only from the front side but alsofrom any oblique direction defined by a large angle while offering anexcellent viewing angle characteristic, a high contrast, and goodquality but not causing gray-scale reversal. On the back side of theliquid crystal panel 100, there are a light source 114 and a light box113 for converting illumination light emanating from the light source114 to light capable of illuminating the liquid-crystal panel 100uniformly.

As shown in FIG. 194, a display screen 110 of this product is turnableand the product is therefore usable as either a sideways display orlengthwise display according to a purpose of use. A switch for use indetecting a tilt by 45° is therefore included. By detecting the state ofthe switch, switching is carried out to select whether display iscarried out for the sideways display or for the lengthwise display. Forthis switching, a mechanism for changing a direction, in which displaydata is read from a frame memory for image display, by 90° is needed.The relevant technology is well-known. The description of the technologywill be omitted.

An advantage provided when the liquid crystal display in accordance withthe present invention is adapted to the above product will be described.Since a conventional liquid crystal display permits only a small viewingangle, when a large display screen is adopted, there arises a problemthat a viewing angle relative to a marginal part of the screen gets solarge that the marginal part becomes hard to see. However, a liquidcrystal display in which the present invention is implemented makes itpossible to view a high-contrast image even at a large viewing anglewithout occurrence of gray-scale reversal. In the product shown in FIG.194, a viewing angle relative to a longer marginal part of the displayscreen becomes large. It has therefore been impossible to adapt a liquidcrystal display to this kind of product. The liquid crystal display ofthe present invention permitting a large viewing angle can be adapted tothe product.

The aforesaid embodiments provide liquid crystal displays in each ofwhich the orientation of a liquid crystal is divided for dividing eachdomain of the liquid crystal mainly into four regions whose azimuths aremutually different in increments of 90°, and liquid crystal displays ineach of which the orientation of a liquid crystal is divided fordividing each domain of the liquid crystal mainly into two regions whoseazimuths are mutually different in increments of 90°. This point will bediscussed in relation to applications of the present invention. When theorientation of a liquid crystal is divided for dividing each domain ofthe liquid crystal into four regions whose azimuths are mutuallydifferent in increments of 90°, a good viewing angle characteristic canbe exhibited in almost all directions. To whichever directions theorientation is set, no problem occurs in particular. For example, whenthe pattern of protrusions shown in FIG. 54 is arranged as shown in FIG.196A relative to a screen, a viewing angle at which display appears wellis 80° or more both in lateral and vertical directions. Even after thescreen is turned and the pattern of protrusions is arranged asillustrated on the right side of FIG. 196A, no problem occurs inparticular.

By contrast, when the orientation of a liquid crystal is divided fordividing each domain thereof into two regions whose azimuths aremutually different by 180°, the viewing angle characteristic will beimproved relative to the directions into which the orientation isdivided but will not be improved very much relative to directionsdifferent from the directions by 90°. When a nearly equal viewing anglecharacteristic is requested to be exhibited in both lateral and verticaldirections, a pattern of protrusions should preferably be, as shown inFIG. 196B, run in an oblique direction in a screen.

Next, a process of manufacturing a liquid crystal display in accordancewith the present invention will be described. In general, the process ofmanufacturing a liquid crystal panel comprises, as described in FIG.197, a step 501 of cleaning substrates, a step 502 of forming gateelectrodes, a step 503 of forming an operating layer by applying acontinuous film, a step 504 of separating devices, a step 505 ofapplying a protective film, a step 506 of forming pixel electrodes, anda step 508 of assembling components which are carried out in that order.For forming insulating protrusions, the step 506 of forming pixelelements is succeeded by a step 507 of forming protrusions.

As shown in FIG. 198, the protrusion forming step comprises a step 511of applying a resist, a step of pre-baking the applied resist, a step513 of exposing a pattern of protrusions so as to leave the positions ofthe protrusions intact, a step 514 of performing development so as toremove portions other than the protrusions, and a step 515 ofpost-baking the remaining protrusions. As described above, at thesubsequent step of applying an alignment film, there is a possibilitythat the resist may react upon the alignment film. At the post-bakingstep 515, baking should therefore be carried out at a high temperatureof a certain level. During the baking, if protrusions are curved to havea cylindrical section, the stability of alignment will increase.

Even when dents are formed as a domain regulating means, nearly the sameprocess as the foregoing one is adopted. However, when electrodes areslitted, a pattern having slitted pixel electrodes should merely becreated at the pixel electrode forming step 506 in FIG. 197. Theprotrusion forming step 507 becomes unnecessary.

What is described in FIG. 198 is an example of drawing a pattern ofprotrusions using a photosensitive resist. The pattern of protrusionsmay be printed. FIG. 199 is a diagram showing a technique of drawing apattern of protrusions by performing letterpress printing. As shown inFIG. 199, a pattern of protrusions is drawn on a flexible relief plate604 made of an APR resin. The relief plate is in turn fixed to thesurface of a large roller 603 referred to as a plate cylinder. The platecylinder is rotated while being interlocked with an anilox roller 605, adoctor roller 606, and a printing stage 602. A polyimide resin solutionused to form protrusions is dropped onto the anilox roller 605 by adispenser 607, and spread by the doctor roller 606 to be developeduniformly over the anilox roller 605. The developed resin solution istransferred to the relief plate 604. The solution transferred to theraised portion of the relief plate 604 is transferred to a substrate 609on the printing stage 602. Thereafter, baking or the like is carriedout. Various techniques of drawing a microscopic pattern by printinghave been employed in practice. If a pattern of protrusions can be drawnusing any of the techniques, the pattern of protrusions can be drawn atlow cost.

Next, injection of a liquid crystal into a liquid-crystal panel to beperformed after upper and lower substrates are bonded will be described.As described in conjunction with FIGS. 18A and 18B, at the step ofassembling components to produce a liquid-crystal panel, after a CFsubstrate and TFT substrates are bonded, a liquid crystal is injected. AVA type TFT LCD has cells whose thickness is small. It takes much timeto inject a liquid crystal. Since protrusions are formed, it takes muchmore time to inject the liquid crystal. It is therefore requested toshorten the time required for injecting the liquid crystal as much aspossible.

FIG. 200 is a diagram showing the configuration of a liquid-crystalinjection apparatus. The details of the apparatus will be omitted. Aninjection connector 615 is attached to a liquid-crystal injection portof a liquid-crystal panel 100, and a liquid crystal is supplied from aliquid-crystal defoamer and pressurizer tank 614. Concurrently, anexhaust connector 618 is connected to a liquid-crystal exhaust port, andthe pressure in the liquid-crystal panel 100 is reduced using a vacuumpump 620 for deaeration so that a liquid crystal can be injectedreadily. A liquid crystal exhausted through the exhaust port isseparated from an air by a liquid-crystal trap 619.

In the first embodiment, as shown in FIGS. 18A and 18B, the protrusions20 are linear and running in a direction parallel to the long side ofthe panel 100. The liquid crystal injection port 102 is formed on ashort side of the panel vertical to the protrusions 20, while theexhaust ports 103 are formed on the other short side thereof opposite tothe side on which the injection port 102 is formed. Likewise, as shownin FIGS. 201A and 201B, when the protrusions 20 are linear and runningin a direction parallel to the short side of the panel 100, preferably,the liquid-crystal injection port 102 is formed on one long side of thepanel vertical to the protrusions 20, and the exhaust ports 103 areformed on the other long side thereof opposite to the long side on whichthe injection port 102 is formed. Moreover, as shown in FIGS. 202A and202B, when the protrusions 20 are zigzagged, the liquid-crystalinjection port 102 is preferably formed on a side of the panel verticalto a direction in which the protrusions 20 are extending. As shown inFIGS. 203A and 203A, the exhaust ports 103 are preferably formed on aside of the panel opposite to the side on which the injection port 102is formed.

During injection of a liquid crystal, foams may be mixed in the liquidcrystal. Once foams are mixed in a liquid crystal, imperfect displayensues. Assuming that a negative liquid crystal and a vertical alignmentfilm are employed, when no voltage is applied, black display appears.Even if foams are mixed in the liquid crystal, black display appears inareas coincident with the foams. The mixing of foams cannot therefore bediscovered in this state. A voltage is applied to electrodes so thatwhite display will appear. When black display does not appear in anyarea, it is confirmed that no foam has mixed in the liquid crystal.However, since there is no electrode near the liquid-crystal injectionport, even if foams are mixed in a portion of the liquid crystal nearthe liquid-crystal injection port, the foams cannot be discovered. Iffoams are present in this portion of the liquid crystal, there is a fearthat the foams will be dispersed to deteriorate display quality. Eventhe foams near the injection port must therefore be discovered. In aliquid crystal display of the present invention, therefore, as shown inFIG. 207, an electrode 120 is formed near an injection port 101 outsidea display area 121 and the black matrices 34 so that mixing of foams inthis portion of a liquid crystal can be detected.

As explained above, the VA system liquid crystal display device usingthe domain regulating means such as the protrusion and the recess, theslit, etc, does not require the rubbing treatment. Therefore,contamination in the manufacturing process can be drastically reduced,and a part of the washing process can be omitted. However, the negativetype (n type) liquid crystal used has lower contamination resistance toorganic materials, particularly to polyurethane resin and the skin, thanthe positive type liquid crystal that is ordinarily used, and involvesthe problem that display defect occurs. This display defect presumablyresults from the drop, of the specific resistance of the contaminatedliquid crystal.

Therefore, examinations are first made as to which size of thepolyurethane resin and the skin causes this display defect. FIGS. 205Ato 205C show the VA system liquid crystal panel. After the verticalalignment film is formed on the two substrates 16 and 17, severalpolyurethane resins having a size of about 10 μm are put on one of thesubstrates. After the spacers 45 are formed on one of the substrates andthe seal material 101, on the other, the substrates are bonded to eachother, and the panel is manufactured by charging the liquid crystal. Asa result, it is found out that the polyurethane resin 700 expands to anarea of 15 μm square by heat and by the formation of the cell thickness(cell gap), and the display defect due to contamination of the liquidcrystal is recognized within the range of 0.5 to 2 mm with thepolyurethane resin 700 as the center.

FIG. 206 shows the result of the investigation of the contamination areaof the liquid crystal by changing the size of the polyurethane resin700. Assuming that no problem occurs when the display has a size of notgreater than 0.3 mm square on the panel, the size of the polyurethaneresin must be not greater than 5 μm. This also holds true of the skin.

As described above, the polyurethane resin and the skin lower thespecific resistance of the liquid crystal, thereby inviting the displaydefect. Therefore, the relationship between the mixing quantity of thepolyurethane resin and the drop of the specific resistance is examined.FIG. 207 shows the calculation result of frequency dependence of anequivalent circuit of the liquid crystal pixel shown in FIG. 208 byassuming the gate-on state. This graph shows the change of the effectivevoltage to the frequency when the resistance is 9.1×10⁹, 9.1×10¹⁰,9.1×10¹¹ and 9.1×10¹² in the equivalent circuit of the liquid crystalpixel. It can be appreciated from the graph that the drop of theresistance value of the liquid crystal causes the drop of the effectivevoltage. It can be appreciated further that abnormal display occurs atthe drop of the specific resistance of at least 3 digits within thefrequency range of 1 to 60 Hz that is associated with the practicaldisplay.

FIGS. 208 and 209 are graphs showing within which time the charge oncestored is discharged when the resistance is 9.1×10¹⁰, 9.1×10¹¹ and9.1×10¹², respectively, by assuming the state where the liquid crystalpixel holds the charge. For reference, an example of the case where onlythe alignment film exists is shown, too. Because the alignment film hasa large resistance and a large time constant, it hardly contributes todischarge phenomenon. FIG. 209 shows in magnification the portion below0.2 s in FIG. 208. It can be seen from this graph that when the liquidcrystal resistance is lower by at least two digits, a black smear startsoccurring at 60 Hz.

It can be understood from the observation described above that theproblem develops when the resistance drops by two to three digits due tothe polyurethane resin and the skin.

Next, after phenyl urethane is charged into the liquid crystal, aultrasonic wave is applied for 10 seconds and the liquid crystal isthereafter left standing so as to measure the specific resistance of thesupernatant. It is found out from the result that the specificresistance drops drastically when the mixing quantity of thepolyurethane resin is about 1/1000 in terms of a molar ratio.

It is concluded from the explanation described above that non-uniformdisplay does not occur at the level at which the mixing quantity of thepolyurethane and the skin is not greater than 1/1000 in terms of themolar ratio.

The embodiments of panels according to the present invention in whichdirections of alignment of liquid crystalline molecules are divided bythe domain regulating means have been described so far. As alreadydescribed, it is known that optical retardation film are available forimproving the view angle performance. Next, embodiments regardingcharacteristics and arrangements of the retardation films will bedescribed. The LCD panels of these embodiments have protrusions shown inFIG. 54. Namely, in the VA LCD panel, the directions of alignment ofliquid crystalline molecules are divided into four areas in each pixel.

FIG. 210 is a diagram showing a constitution of a prior art VA LCD. Aspace formed between two electroded 12, 13 is sealed with a liquidcrystal material. Thus a liquid crystal panel is completed. As shown inFIG. 210, a first polarizing plate 11 and a second polarizing plate 15are arranged at both sides of the panel. In the VA LCD, verticalalignment films are formed on the electrodes and the liquid crystal hasnegative dielectric constant anisotoropy. The rubbing directions of thetwo vertical alignment films are different each other by 180 degrees.Further, the rubbing directions intersects with the absorption axis ofthe polarizing plates. Namely, the VA LVD panel is that shown in FIGS.7A to 7C. FIG. 211 shows isocontrast curves. FIG. 212 shows viewingangle regions, in each of which gray-scale reversal occurs during aneight-gray-scale level driving operation in such a case. From theseresults, contrasts at directions of 0°, 90°, 180° and 270° are low andthe gray-scale reversal occurs in wide view-angle.

FIG. 213 shows a constitution of a VA mode LCD device in whichprotrusion patterns as illustrated in FIG. 54 are formed.

FIG. 214 shows iso-contrast curves in the case of the LCD device shownin FIG. 213. Further, FIG. 215 shows viewing angle regions, in each ofwhich gray-scale reversal occurs during an eight-gray-scale-leveldriving operation, in the case of such a liquid crystal display device.These figures reveal that although the gray-scale reversal is improvedin the case of this device as compared with the case of the conventionaldevice of the VA (vertically aligned) type, the improvement on thegray-scale reversal is insufficient and that the contrast is notimproved very much.

Applicant of the present application disclosed in Japanese PatentApplication No. 8-41926/1996 and Japanese Patent Application Nos.9-29455/1997 and 8-259872/1996, whose priority is based on the JapanesePatent Application No. 8-41926/1996 that the viewing anglecharacteristics of a liquid crystal display device of the VA type, onwhich the alignment division is performed by rubbing, are improved byproviding an optical retardation film (namely, a phase difference film)therein. These Japanese Patent Applications, however, do not refer tothe cases of performing the alignment division by protrusions,depressions (or dents) or slits respectively provided in pixelelectrodes.

In the following, conditions for further improving the viewing anglecharacteristics of a liquid crystal display device of the VA type, whichis adapted to perform the alignment division in each pixel through theuse of protrusions, depressions or slits provided in the pixelelectrodes, by providing an optical retardation film therein will bedescribed.

First, the optical retardation film used in the device of the presentinvention will be described hereinbelow by referring to FIG. 216. Asillustrated in FIG. 216, let n_(x) and n_(y) designate dielectricconstantes (or indices) respectively corresponding to inplane directionsdefined in a surface of the film. Further, let n_(z) denote a dielectricconstant in the direction of thickness thereof. The following relationamong the dielectric constantes n_(x), n_(y) and n_(z) holds in thephase difference film to be used in the device of the present invention:n_(x), n_(y)≧n_(z).

Incidentally, an optical retardation film, in which the followingrelation holds: n_(x)

n_(y)=n_(z), has optically positive uniaxiality therein. Hereunder, sucha phase difference film will be referred to simply as a positiveuniaxial film. Axis extending in a direction corresponding to a largerone of the dielectric constantes n_(x) and n_(y) is referred to as aphase lag axis. In this case, n_(x)

n_(y). Therefore, the axis extending in the x-direction is referred toas the phase lag axis. Let d designate the thickness of the film. Whenlight passes through this positive uniaxial film, the following phasedifference (or optical retardation) R is caused in an inplane direction:R=(n_(x)−n_(y))d. Hereinafter, the “phase difference caused by thepositive uniaxial film” indicates a phase difference caused in aninplane direction.

Moreover, a phase difference film, in which the following relationholds: n_(x)=n_(y)

n_(z), has optically negative uniaxiality in the direction of a normalto the surface thereof. Hereunder, such a phase difference film will bereferred to simply as a negative uniaxial film. Let d designate thethickness of the film. When light passes through this negative uniaxialfilm, the following phase difference R is caused in the direction of thethickness thereof: R=((n_(x)+n_(y))/2−n_(z))d. Hereinafter, the “phasedifference caused by the negative uniaxial film” indicates a phasedifference caused in the direction of the thickness thereof.

Furthermore, a phase difference film, in which the following relationholds: n_(x)

n_(y)

n_(z), has (optical) biaxiality. Hereunder, such a phase difference filmwill be referred to simply as a biaxial film. In this case, n_(x)

n_(y). Therefore, the axis extending in the x-direction is referred toas the phase lag axis. Let d designate the thickness of the film. Whenlight passes through this positive uniaxial film, the following phasedifference R is caused in an inplane direction: R=(n_(x)−n_(y))d(incidentally, n_(x)

n_(y)). Further, the phase difference R caused in the direction of thethickness thereof is predetermined by the following equation:

R=((n _(x) +n _(y))/2−n _(z))d.

FIG. 217 is a diagram showing the constitution of a liquid crystaldisplay device which is a 52th embodiment of the present invention.

Color filter and a common electrode (namely, what is called afull-surface covering electrode) are formed on the liquid-crystal-sidesurface of CF (Color Filter) substrate that is one of substrates 91 and92. Further, TFT elements, bus lines and pixel electrodes are formed onthe liquid-crystal-side surface of TFT substrate that is the other ofthe substrates 91 and 92.

Vertical alignment film is formed on the liquid-crystal-side surfaces ofthe substrates 91 and 92 by applying a vertical alignment materialthereto through transfer printing, and by then burn the material at 180°C. Subsequently, a positive photosensitive overcoating (or protecting)material is applied onto the vertical alignment film through spincoating. Then, a protrusion pattern shown in FIG. 54 is formed byperforming prebaking, exposure and postbaking.

The substrates 91 and 92 are bonded together through a spacer having adiameter of 3.5 μm. Further, a space formed therebetween is sealed witha liquid crystal material having negative dielectric constantanisotropy. Thus a liquid crystal panel is completed.

As illustrated in FIG. 217, the liquid crystal display device, which isthe 52th embodiment of the present invention, is constituted by placinga first polarizing plate 11, a first positive uniaxial film 94, twosubstrates 91 and 92, a second positive uniaxial film 94 and a secondpolarizing plate 15 therein in this order. Incidentally, the first andsecond uniaxial films 94 are placed so that the phase lag axis of thefirst positive uniaxial film 94 intersects with the absorption axis ofthe first polarizing plate 11 at right angles.

FIG. 218 shows iso-contrast curves in the case that each of the phasedifferences R₀ and R₁ respectively corresponding to the first and secondpositive uniaxial films 61 of the 52th embodiment is set at 110 nm.Further, FIG. 219 shows viewing angle regions, in each of whichgray-scale inversion occurs during an eight-gray-scale-level drivingoperation in such a case. As is apparent from the comparison with FIGS.214 and 215, a range, in which high contrast is obtained, is enlargedextensively, with the result that the gray-scale reversal does not occurin the entire viewing angle region. Consequently, the viewing anglecharacteristics are considerably improved.

Incidentally, the viewing angle characteristics were studied by changingthe retardation R₀ and R₁ in various ways in the case of theconstitution of FIG. 217. Process of studying the viewing angle was asfollows. First, while changing the phase differences R₀ and R₁, an angleat which the contrast (ratio) was 10, was found in each of an upperright direction (corresponding to an azimuth angle of 45° towards theright top), an upper left direction (corresponding to an azimuth angleof 135° towards the left top), a lower left direction (corresponding toan azimuth angle of 225° towards the left bottom) and a lower rightdirection (corresponding to an azimuth angle of 315° towards the rightbottom) with respect to the liquid crystal panel, as viewed in thisfigure. FIG. 220 is a contour graph showing each contour that connectspoints, each of which is represented by coordinates R₀ and R₁ thereofand corresponds to the found angle having a same value. Incidentally,the contour graphs respectively corresponding to the upper rightdirection, the upper left direction, the lower left direction and thelower right direction were the same with one another. It is consideredthat this was because four regions obtained by the alignment divisionwere equivalent to one another as a result of using the protrusionpattern shown in FIG. 54.

In the case of FIG. 217, the angle, at which the contrast ratio is 10 ineach of the directions respectively corresponding to the azimuth angles45°, 135°, 225° and 315°, is 39°. This reveals that the use of theoptical retardation film is effective in the case of the combination ofthe coordinates R₀ and R₁ shown in FIG. 223. Incidentally, in the caseillustrated in FIG. 223, the angle, at which the contrast ratio is 10,is not less than 39° when R₀ and R₁ meet the following conditions orrequirements:

R ₁≦450 nm−R ₀ , R ₀−250 nm≦R ₁ ≦R ₀+250 nm, 0≦R₀ and 0≦R₁.

Additionally, the retardation Δn·d caused in a liquid crystal waschanged within a piratical range. Moreover, the twist angle was changedwithin a range of 0 to 90°. Similarly, the optimum conditions for R₀ andR₁ were obtained. As a result, it was ascertained that the optimumconditions were the same as the aforementioned requirements even in suchcases.

FIG. 221 is a diagram showing the constitution of a liquid crystaldisplay device which is a 53rd embodiment of the present invention. Thisembodiment is different from the 52nd embodiment in that two positiveuniaxial films, namely, first and second positive uniaxial films 94 areplaced between the first polarizing plate 11 and the liquid crystalpanel, that the phase lag axes of the two positive uniaxial films 94intersect with each other at right angles and that the phase lag axis ofthe second positive uniaxial film adjoining the first polarizing plate11 intersects with the absorption axis of the first polarizing plate 11at right angles.

FIG. 222 shows iso-contrast curves in the case that the phasedifferences R₀ and R₁ respectively corresponding to the first and secondpositive uniaxial films 61 of the 52nd embodiment are set at 110 nm and270 nm, respectively. Further, FIG. 223 shows viewing angle regions, ineach of which gray-scale inversion-occurs during aneight-gray-scale-level driving operation in such a case. As is obviousfrom the comparison with FIGS. 214 and 215, a range, in which highcontrast is obtained, is enlarged extensively. Moreover, the range, inwhich the gray-scale reversal occurs, is greatly reduced. Consequently,the viewing angle characteristics are considerably improved.

FIG. 224 shows the viewing angle characteristics obtained as a result ofbeing studied by changing the phase differences R₀ and R₁ of the firstand second uniaxial films 94 in various ways in the case of theconstitution of FIG. 221, similarly as in the case of the 52thembodiment. The viewing angle characteristics shown in FIG. 224 are thesame as of FIG. 220 and are illustrated by a contour graph showingangles, at which the contrast ratio is 10, in terms of coordinates R₀and R₁. As is seen therefrom, the angle, at which the contrast ratio is10, is not less than 39° when R₀ and R₁ meet the following conditions orrequirements:

2R ₀−170 nm≦R ₁≦2R ₀+280 nm,

R ₁ ≦−R ₀/2+800 nm, 0≦R₀ and 0≦R₁.

Further, it was ascertained that the optimum conditions were the same asthe aforementioned requirements even in the cases where, similarly, inthe case of the 53th embodiment, the retardation Δn·d caused in a liquidcrystal was changed within a practical range and where, moreover, thetwist angle was changed within a range of 0 to 90°.

FIG. 225 is a diagram showing the constitution of a liquid crystaldisplay device which is a 54th embodiment of the present invention.

This embodiment is different from the 52th embodiment in that the firstnegative uniaxial film 95 is placed between the liquid crystal panel andthe first polarizing plate 11 and that the second negative uniaxial film95 is placed between the liquid crystal panel and the second polarizingplate 15.

FIG. 226 shows the viewing angle characteristics obtained as a result ofbeing studied by changing the phase differences R₀ and R₁ in variousways in the case of the constitution of FIG. 225, similarly as in thecase of the 52th embodiment. The viewing angle characteristics shown inFIG. 226 are the same as of FIG. 220 and are illustrated by a contourgraph showing angles, at which the contrast ratio is 10, in terms ofcoordinates R₀ and R₁. As is seen therefrom, the angle, at which thecontrast ratio is 10, is not less than 39° when R₀ and R₁ meet thefollowing condition or requirement:

R ₀ +R ₁≦500 nm.

Incidentally, similarly, in the case of the 54th embodiment, theretardation Δn·d caused in a liquid crystal and the upper limit to theoptimum condition were studied by changing the retardation Δn·d within apractical range. FIG. 227 illustrate results of this study. Let R_(LC)denote Δn·d caused in the liquid crystal. Consequently, the optimumvalue in the optimum condition for a sum of the phase differencesrespectively corresponding to the phase difference films is not morethan (1.7×R_(LC)+50) nm.

Further, although this characteristic condition relates to the contrast(ratio), the optimum condition for the gray-scale reversal was similarlystudied. Angles, at which gray-scale reversal occurs, were found bychanging the phase differences R₀ and R₁ in the direction of thethickness of the first and second negative uniaxial films 95 in variousmanners in the constitution of FIG. 225, similarly as in the case of thecontrast ratio. FIG. 228 shows contour graphs obtained from the foundangles, which is illustrated by using the coordinates R₀ and R₁.Incidentally, the angle, at which the gray-scale reversal occurs in thecase illustrated in FIG. 215, is 52°. Thus, when the phase differencesR₀ and R₁ have values at which the angle enabling an occurrence of thegray-scale reversal is not less than 52° in the case illustrated in FIG.228, the phase difference film has an effect on the gray-scale reversal.In the case shown in FIG. 228, the angle, at which the contrast ratio is10, is not less than 39° when R₀ and R₁ meet the following condition orrequirement:

R ₀ +R ₁≦345 nm.

Then, in the case of the 54th embodiment, the relation between Δn·dcaused in a liquid crystal (display) cell and the upper limit to theoptimum condition was studied by changing the retardation Δn·d within apractical range. FIG. 229 illustrate results of this study. This revealsthat the upper limit to the optimal condition is nearly constantindependent of Δn·d caused in the liquid crystal cell and that theoptimum condition for a sum of the phase differences respectivelycorresponding to the phase difference films is not more than 350 nm.

It is desirable that the angle, at which the contrast ratio is not lessthan 50°. Further, in view of the gray-scale reversal and Δn·d caused inthe liquid crystal cell, it is preferable that a sum of the phasedifferences respectively corresponding to the phase difference films isnot less than 30 nm but is not more than 270 nm.

Moreover, as a result of studying the optimal condition by changing thetwist angle in a range of 0 to 90°, it is found that the optimumcondition was the same as the aforementioned requirement.

A 55th embodiment of the present invention is obtained by removing oneof the first and second negative uniaxial films 95 from the constitutionof the liquid crystal display device of FIG. 225, which is the thirdembodiment of the present invention.

FIG. 230 shows iso-contrast curves in the case that the phase differencecorresponding to one of the negative uniaxial films 95 of the 55thembodiment is set at 200 nm. Further, FIG. 231 shows viewing angleregions, in each of which gray-scale inversion occurs during aneight-gray-scale-level driving operation in such a case. As is obviousfrom the comparison with FIGS. 214 and 215, a range, in which highcontrast is obtained, is enlarged extensively. Moreover, the range, inwhich the gray-scale reversal occurs, is greatly reduced. Consequently,the viewing angle characteristics are considerably improved. Moreover,the optimal condition for realizing the contrast ratio of 10 and theoptimal condition for the gray-scale reversal were studied. Results ofthis study reveal that it is sufficient to use a single negativeuniaxial film having the phase difference corresponding to a sum of thephase differences of the negative uniaxial films of the 54th embodiment.

Each of 56th to 58th embodiments of the present invention uses thecombination of positive and negative uniaxial films. Although there arevarious kinds of modifications to the arrangement of such films, it hasbeen found that the constitutions of the fifth to seventh embodimentshave (advantageous) effects.

FIG. 232 is a diagram showing the constitution of a liquid crystaldisplay device which is a 56th embodiment of the present invention.

The 56th embodiment differs from the 52th embodiment in that a negativeuniaxial film 95 is used and placed between the liquid crystal panel andthe first polarizing plate 11 instead of the first positive uniaxialfilm 94.

FIG. 233 shows iso-contrast curves in the case that the phase differenceR₀ in an inplane direction in the surface of the positive uniaxial film94 and the phase difference R₁ in the direction of thickness of thenegative uniaxial film 95 are set at 150 nm in the 56th embodiment.Further, FIG. 234 shows viewing angle regions, in each of whichgray-scale inversion occurs during an eight-gray-scale-level drivingoperation in such a case. As is obvious from the comparison with FIGS.214 and 215, a range, in which high contrast is obtained, is enlargedextensively. Moreover, the range, in which the gray-scale reversaloccurs, is greatly reduced. Consequently, the viewing anglecharacteristics are considerably improved.

In the case of the 56th embodiment, the optimal condition for thecontrast was studied. FIG. 235 shows results of this study, which revealthat the optimum condition indicated by FIG. 235 was the same asillustrated in FIG. 220.

FIG. 236 is a diagram showing the constitution of a liquid crystaldisplay device which is a 57th embodiment of the present invention. Thisembodiment is different from the 52th embodiment in that a positiveuniaxial films 61 are placed between the liquid crystal panel and thefirst polarizing plate 11 and that a negative uniaxial film 95 is placedbetween this positive uniaxial film 94 and the first polarizing plate11. The positive uniaxial film 94 is placed in such a manner that thephase lag axis thereof intersects with the absorption axis of the firstpolarizing plate 11 at right angles.

FIG. 237 shows iso-contrast curves in the case that the phase differenceR₀ in an inplane direction in the surface of the positive uniaxial film61 and the phase difference R₁ in the direction of thickness of thenegative uniaxial film 62 are set at 50 nm and 150 nm in the 57thembodiment, respectively. Further, FIG. 238 shows viewing angle regions,in each of which gray-scale inversion occurs during aneight-gray-scale-level driving operation in such a case. As is obviousfrom the comparison with FIGS. 214 and 215, a range, in which highcontrast is obtained, is enlarged extensively. Moreover, the range, inwhich the gray-scale reversal occurs, is greatly reduced. Consequently,the viewing angle characteristics are considerably improved.

Even in the case of the 57th embodiment, the optimal condition for thecontrast was studied. FIG. 239 shows results of this study, which revealthat the optimum condition indicated by FIG. 239 was the same asillustrated in FIG. 220.

FIG. 240 is a diagram showing the constitution of a liquid crystaldisplay device which is a 58th embodiment of the present invention. Thisembodiment is different from the 52th embodiment in that a negativeuniaxial films 95 are placed between the liquid crystal panel and thefirst polarizing plate 11 and that a positive uniaxial film 94 is placedbetween this negative uniaxial film 95 and the first polarizing plate11. The positive uniaxial film 94 is placed in such a manner that thephase lag axis thereof intersects with the absorption axis of the firstpolarizing plate 11 at right angles.

FIG. 241 shows iso-contrast curves in the case that the phase differenceR₁ in an inplane direction in the surface of the positive uniaxial film94 and the phase difference R₀ in the direction of thickness of thenegative uniaxial film 95 are set at 150 nm in the 58th embodiment.Further, FIG. 242 shows viewing angle regions, in each of whichgray-scale inversion occurs during an eight-gray-scale-level drivingoperation in such a case. As is obvious from the comparison with FIGS.214 and 215, a range, in which high contrast is obtained, is enlargedextensively. Moreover, the range, in which the gray-scale reversaloccurs, is greatly reduced. Consequently, the viewing anglecharacteristics are considerably improved.

Even in the case of the 58th embodiment, the optimal condition for thecontrast was studied. FIG. 243 shows results of this study, which revealthat the optimum condition indicated by FIG. 243 was the same asillustrated in FIG. 220.

FIG. 244 is a diagram showing the constitution of a liquid crystaldisplay device which is an 59th embodiment of the present invention.

This embodiment is different from the 52nd embodiment in that a phasedifference film 96, whose inplane dielectric constantes n_(x) and n_(y)and dielectric constant n_(z) in the direction of thickness thereof havethe following relation: n_(x), n_(y)≧n_(x), is placed between the liquidcrystal panel and the first polarizing plate 11 and that a positiveuniaxial film 94 is removed from between the liquid crystal panel andthe second polarizing plate 15. The phase difference film 96 is placedin such a manner that the x-axis thereof intersect with the absorptionaxis of the first polarizing plate 11 at right angles.

FIG. 245 shows iso-contrast curves in the case that the x-axis isemployed as the phase lag axis of the phase difference film 96, namely,n_(x)

n_(y) and that the phase difference in an inplane direction in thesurface of the film and the phase difference in the direction ofthickness thereof are set at 55 nm and 190 nm, respectively, in the 59thembodiment. Further, FIG. 246 shows viewing angle regions, in each ofwhich gray-scale inversion occurs during an eight-gray-scale-leveldriving operation in such a case. As is obvious from the comparison withFIGS. 214 and 215, a range, in which high contrast is obtained, isenlarged extensively. Moreover, the range, in which the gray-scalereversal occurs, is greatly reduced. Consequently, the viewing anglecharacteristics are considerably improved.

Incidentally, quantities R_(xy) and R_(yz) are defined as follows:R_(xy)=(n_(x)−n_(y))d; and R_(yz)=(n_(y)−n_(z))d. In the case of the59th embodiment, the optimal condition for the contrast (ratio) wasstudied by changing the quantities R_(xy) and R_(yz) in various ways.FIG. 247 shows the found optimal condition for the contrast. The optimumcondition shown in FIG. 247 was the same as the aforementioned condition(of FIG. 220), except that R₀ and R₁ correspond to R_(xy) and R_(yz),respectively. These results reveal that the angles, at which thecontrast ratio is 10, are not less than 39° when the quantities R_(xy)and R_(yz) satisfy the following conditions:

R _(xz)−250 nm≦R _(yz) ≦R _(xz)+150 nm,

R _(yz) ≦−R _(xz)+1000 nm,

Incidentally, let R₀ and R₁ denote the phase difference in an inplanedirection of the phase difference film 96 and the phase difference inthe direction of thickness thereof, respectively. Thus, the followingrelations hold for these phase differences:

R ₀=(n _(x) −n _(y))d=R _(xz) −R _(yz) . . . (in the case thatn_(x)≧n_(y));

R ₀=(n _(y) −n _(x))d=R _(yz) R _(xz) . . . (in the case thatn_(y)≧n_(x));

and

R _(yz)=((n _(x) +n _(y))/2−n _(z))d=(R _(xz) −R _(yz))/2.

Therefore, the optimal conditions for R_(xz) and R_(yz) are written asfollows:

R₀≦250 nm, R₁≦500 nm.

Namely, it is desirable that the inplane phase difference is not morethan 250 nm and the phase difference in the direction of thickness ofthe film is not more than 500 nm and that the biaxial phase differencefilm is placed so that the phase lag axis thereof intersects with theabsorption axis of the adjacent polarizing plate at right angles.

As a result of studying the relation between the retardation Δn·d causedin a liquid crystal cell and the upper limit to the optimal condition bychanging the retardation Δn·d in various way within a practical range,it was found that the optimal condition for the phase difference in aninplane direction was not more than 250-nm regardless of the retardationΔn·d caused in a liquid crystal cell. In contrast, the phase differencein the direction of thickness depends on the retardation Δn·d caused ina liquid crystal cell. FIG. 248 shows the results of the study on therelation between the retardation Δn·d caused in a liquid crystal celland the upper limit to the optimal range of the phase difference in thedirection of thickness of the film. Let R_(LC) denote Δn·d caused in theliquid crystal. Consequently, it is concluded that the optimum value inthe optimal condition for the phase difference in the direction ofthickness of the phase difference film is not more than (1.7×R_(LC)+50)nm.

Incidentally, the optimal condition in the case of a configuration, inwhich a plurality of phase difference films 96 were placed in at leastone of spaces formed between the liquid crystal panel and one of thefirst polarizing plate 11 and the second polarizing plate 15, which wereprovided at one or both of sides of the liquid crystal panel, andbetween the liquid crystal panel and the other thereof was studiedsimilarly. As a result, it was found that the optimum condition was thecase where the phase difference in the inplane direction of each of thephase difference films 96 was not more than 250 nm and that a sum of thephase differences in the direction of thickness of the phase differencefilms 96 was not more than (1.7×R_(LC)+50) nm.

Further, as a result of studying the optimal condition similarly bychanging the twist angle in a range of 0 to 90°, it was found that theoptimum condition was the same as the aforementioned requirement.

A positive uniaxial film (n_(x)

n_(y)=n_(z)), a negative uniaxial film (n_(x)=n_(y)

n_(z)) and a biaxial film (n_(x)

n_(y)

n_(z)) are employed as the film 96. Namely, a single or a combination ofsuch films may be used.

In the foregoing description, there has been described the optimalconditions for the phase difference film in the case that alignmentdivision is performed in a pixel by providing rows of protrusions on theliquid-crystal-side of each of the two substrates composing the liquidcrystal panel. However, even in the case of performing the alignmentdivision by using depressions or slits formed in the pixel electrodes,the viewing angle characteristics can be improved on the similarconditions.

Further, in the present specification, the polarizing plates have beendescribed as ideal ones. Therefore, it is obvious that the phasedifference (incidentally, the phase difference in the direction ofthickness of the film is usually about 50 nm) caused by a film (namely,TAC (cellulose triacetate) film) protecting a polarizer should besynthesized with the phase difference caused by the phase differencefilm of the present invention.

Namely, the provision of the phase difference film may be omittedapparently by making TAC film meet the conditions according to thepresent invention. However, in this case, needless to say, such TAC filmperforms as well as the phase difference film of the present invention,which should be added to the device, does.

The embodiments in which the present invention is implemented in a TFTliquid crystal display have been described. The present invention canalso be implemented in liquid crystal displays of other types. Forexample, the present invention can be implemented in a MOSFET LCD of areflection type but not of the TFT type or in a mode using a diode suchas a MIM device as an active device. Moreover, the present invention canbe implemented in both a TFT mode using an amorphous silicon and a TFTmode using a polycrystalline silicon. Furthermore, the present inventioncan be implemented in not only a transmission type LCD but also areflection type or plasma-addressing type LCD.

An existing TN LCD has a problem that it can cover only a narrow rangeof viewing angles. An IPS LCD exhibiting an improved viewing anglecharacteristic has problems that a response speed it can offer is nothigh enough and it cannot therefore be used to display a motion picture.Implementation of the present invention can solve these problems, andrealize an LCD exhibiting the same viewing angle characteristic as theIPS LCD and offering a high response speed surpassing the one offered bythe TN LCD. Moreover, the LCD can be realized merely by formingprotrusions on substrates or slitting electrodes, and can therefore bemanufactured readily. Besides, the rubbing step and after-rubbingcleaning step which are required for manufacturing the existing TN LCDand IPS LCD become unnecessary. Since these steps cause imperfectalignment, an effect of improving a yield and product reliability canalso be exerted.

Since the LCD offering a high operating speed and exhibiting a goodviewing angle characteristic can be realized, expansion of anapplication range including the application to a monitor substitutingfor the CRT is expected.

1. A liquid crystal display device comprising: a common electrodeprovided on a first substrate; a pixel electrode provided on a secondsubstrate; a liquid crystal layer including a liquid crystal having anegative dielectric constant anisotropy, provided between said first andsecond substrates, wherein liquid crystal molecules align in a directionvertical to the first and second substrates when no voltage is applied;and first and second alignment control structures formed, respectively,on said first substrate and said second substrate, for regulatingazimuths of orientations of said liquid crystal when a voltage isapplied to said liquid crystal, said first and second alignment controlstructures each including a first line portion and a second lineportion; wherein said first line portion extends in a first direction,and said second line portion extends in a second direction differentfrom said first direction, wherein said pixel electrode includes an edgeextending in a direction different from both said first direction andsaid second direction, and wherein said pixel electrode also has twoadditional edges extending parallel to each other, each of the twoadditional edges including a first portion extending in said firstdirection and a second portion extending in said second direction.